<?xml version="1.0" encoding="US-ASCII"?>
<!-- DFIN New ActiveDisclosure (SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-03-30T12:17:47.3083+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheets" xlink:href="revb-20221231.xsd#StatementConsolidatedBalanceSheets" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheetsParentheticals" xlink:href="revb-20221231.xsd#StatementConsolidatedBalanceSheetsParentheticals" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfChangesInStockholdersEquityDeficit" xlink:href="revb-20221231.xsd#StatementConsolidatedStatementsOfChangesInStockholdersEquityDeficit" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfCashFlows" xlink:href="revb-20221231.xsd#StatementConsolidatedStatementsOfCashFlows" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsTables" xlink:href="revb-20221231.xsd#DisclosureWarrantsTables" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureOrganizationAndBasisOfPresentationDetails" xlink:href="revb-20221231.xsd#DisclosureOrganizationAndBasisOfPresentationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureBusinessCombinationDetails" xlink:href="revb-20221231.xsd#DisclosureBusinessCombinationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureBalanceSheetDetailsScheduleOfAccruedExpensesDetails" xlink:href="revb-20221231.xsd#DisclosureBalanceSheetDetailsScheduleOfAccruedExpensesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/revb_r_CommitmentsandContingenciesDetails" xlink:href="revb-20221231.xsd#revb_r_CommitmentsandContingenciesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePipeInvestmentDetails" xlink:href="revb-20221231.xsd#DisclosurePipeInvestmentDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePublicOfferingDetails" xlink:href="revb-20221231.xsd#DisclosurePublicOfferingDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePreferredStockDetails" xlink:href="revb-20221231.xsd#DisclosurePreferredStockDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureUnitsDetails" xlink:href="revb-20221231.xsd#DisclosureUnitsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureCommonStockDetails" xlink:href="revb-20221231.xsd#DisclosureCommonStockDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureCommonStockSummaryOfTotalSharesOfCommonStockReservedForIssuanceDetails" xlink:href="revb-20221231.xsd#DisclosureCommonStockSummaryOfTotalSharesOfCommonStockReservedForIssuanceDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationDetails" xlink:href="revb-20221231.xsd#DisclosureStockbasedCompensationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationScheduleOfStockOptionsActivityDetails" xlink:href="revb-20221231.xsd#DisclosureStockbasedCompensationScheduleOfStockOptionsActivityDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationAssumptionsUsedInEstimatingFairValueOfStockOptionsDetails" xlink:href="revb-20221231.xsd#DisclosureStockbasedCompensationAssumptionsUsedInEstimatingFairValueOfStockOptionsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationSummaryOfStockbasedCompensationExpenseDetails" xlink:href="revb-20221231.xsd#DisclosureStockbasedCompensationSummaryOfStockbasedCompensationExpenseDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsDetails" xlink:href="revb-20221231.xsd#DisclosureWarrantsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsScheduleOfFairValueOfWarrantsEstimatedUsingBlackscholesOptionPricingModelDetails" xlink:href="revb-20221231.xsd#DisclosureWarrantsScheduleOfFairValueOfWarrantsEstimatedUsingBlackscholesOptionPricingModelDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/revb_r_IncomeTaxesDetails" xlink:href="revb-20221231.xsd#revb_r_IncomeTaxesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://revbiosciences.com/20221231/taxonomy/role/DisclosureSubsequentEventsDetails" xlink:href="revb-20221231.xsd#DisclosureSubsequentEventsDetails" xlink:type="simple"/>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheets">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SubSeriesAPreferredStockMember" xlink:label="revb_SubSeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredOfferingCosts" xlink:label="us-gaap_DeferredOfferingCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SubSeriesA1PreferredStockMember" xlink:label="revb_SubSeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_DeferredUnderwritingCommissions" xlink:label="revb_DeferredUnderwritingCommissions"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_PreferredStockValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsCurrentAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SubSeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_CommonStockValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_DeferredOfferingCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SubSeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommitmentsAndContingencies" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AdditionalPaidInCapital" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_Liabilities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_OperatingLeaseLiabilityCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Assets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="revb_DeferredUnderwritingCommissions" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheetsParentheticals">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SubSeriesAPreferredStockMember" xlink:label="revb_SubSeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SubSeriesA1PreferredStockMember" xlink:label="revb_SubSeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockLiquidationPreferenceValue" xlink:label="us-gaap_PreferredStockLiquidationPreferenceValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SubSeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SubSeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockLiquidationPreferenceValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfChangesInStockholdersEquityDeficit">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_July2022PublicOfferingMember" xlink:label="revb_July2022PublicOfferingMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementAxis" xlink:label="srt_RestatementAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain" xlink:label="srt_RestatementDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain" xlink:label="srt_RestatementDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="srt_ScenarioPreviouslyReportedMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockMember" xlink:label="us-gaap_PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SeriesA1PreferredStockMember" xlink:label="revb_SeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RetrospectiveApplicationOfReversesRecapitalization" xlink:label="revb_RetrospectiveApplicationOfReversesRecapitalization"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RetrospectiveApplicationOfReversesRecapitalizationShares" xlink:label="revb_RetrospectiveApplicationOfReversesRecapitalizationShares"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockIssuedDuringPeriodValueReverseStockSplits" xlink:label="revb_StockIssuedDuringPeriodValueReverseStockSplits"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ReverseStockSplitFractionStockRoundUp" xlink:label="revb_ReverseStockSplitFractionStockRoundUp"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ReverseStockSplitFractionStockRoundUpShares" xlink:label="revb_ReverseStockSplitFractionStockRoundUpShares"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ConversionOfSubSeriesAPreferredStockToCommonStock" xlink:label="revb_ConversionOfSubSeriesAPreferredStockToCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ConversionOfSubSeriesAPreferredStockToCommonStockShares" xlink:label="revb_ConversionOfSubSeriesAPreferredStockToCommonStockShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ConversionOfSubSeriesA1PreferredStockToCommonStock" xlink:label="revb_ConversionOfSubSeriesA1PreferredStockToCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ConversionOfSubSeriesA1PreferredStockToCommonStockShares" xlink:label="revb_ConversionOfSubSeriesA1PreferredStockToCommonStockShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNet" xlink:label="revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNet"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNetShares" xlink:label="revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNetShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_EquityIssuanceForFeesInConnectionWithBusinessCombination" xlink:label="revb_EquityIssuanceForFeesInConnectionWithBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_EquityIssuanceForFeesInConnectionWithBusinessCombinationShares" xlink:label="revb_EquityIssuanceForFeesInConnectionWithBusinessCombinationShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombination" xlink:label="revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombinationShares" xlink:label="revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombinationShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockIssuedDuringPeriodValueNewIssuanceOfSubSeriesA1PreferredStock" xlink:label="revb_StockIssuedDuringPeriodValueNewIssuanceOfSubSeriesA1PreferredStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockIssuedDuringPeriodSharesNewIssuanceOfSubSeriesA1PreferredStock" xlink:label="revb_StockIssuedDuringPeriodSharesNewIssuanceOfSubSeriesA1PreferredStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromPipeInvestmentNet" xlink:label="revb_ProceedsFromPipeInvestmentNet"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromPipeInvestmentNetShares" xlink:label="revb_ProceedsFromPipeInvestmentNetShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantExercise" xlink:label="revb_RolloverWarrantExercise"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantExerciseShares" xlink:label="revb_RolloverWarrantExerciseShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RepurchaseForTheForwardSharePurchaseAgreementExercise" xlink:label="revb_RepurchaseForTheForwardSharePurchaseAgreementExercise"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RepurchaseForForwardSharePurchaseAgreementExerciseShares" xlink:label="revb_RepurchaseForForwardSharePurchaseAgreementExerciseShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsExercise" xlink:label="revb_PreFundedWarrantsExercise"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsExerciseShares" xlink:label="revb_PreFundedWarrantsExerciseShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PaymentForSeriesAPreferredStockSubscribed" xlink:label="revb_PaymentForSeriesAPreferredStockSubscribed"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PaymentForSubSeriesAPreferredStockSubscribed" xlink:label="revb_PaymentForSubSeriesAPreferredStockSubscribed"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PaymentForCommonStockSubscribed" xlink:label="revb_PaymentForCommonStockSubscribed"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfCommonStockForAccruedExpensesInConnectionWithTheBusinessCombination" xlink:label="revb_IssuanceOfCommonStockForAccruedExpensesInConnectionWithTheBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockIssuedDuringPeriodShareNewIssuanceOfSeriesAPreferredStock" xlink:label="revb_StockIssuedDuringPeriodShareNewIssuanceOfSeriesAPreferredStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="revb_July2022PublicOfferingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RestatementAxis" xlink:to="srt_RestatementDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RestatementAxis" xlink:to="srt_RestatementDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RestatementDomain" xlink:to="srt_ScenarioPreviouslyReportedMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RestatementAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RetrospectiveApplicationOfReversesRecapitalization" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RetrospectiveApplicationOfReversesRecapitalizationShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_StockIssuedDuringPeriodValueReverseStockSplits" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ReverseStockSplitFractionStockRoundUp" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ReverseStockSplitFractionStockRoundUpShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ConversionOfSubSeriesAPreferredStockToCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ConversionOfSubSeriesAPreferredStockToCommonStockShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ConversionOfSubSeriesA1PreferredStockToCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ConversionOfSubSeriesA1PreferredStockToCommonStockShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_IssuanceOfCommonStockInConnectionWithTheBusinessCombinationNetShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_EquityIssuanceForFeesInConnectionWithBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_EquityIssuanceForFeesInConnectionWithBusinessCombinationShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_IssuanceOfCommonStockForFeesInConnectionWithBusinessCombinationShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_StockIssuedDuringPeriodValueNewIssuanceOfSubSeriesA1PreferredStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_StockIssuedDuringPeriodSharesNewIssuanceOfSubSeriesA1PreferredStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ProceedsFromPipeInvestmentNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_ProceedsFromPipeInvestmentNetShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RolloverWarrantExercise" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RolloverWarrantExerciseShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RepurchaseForTheForwardSharePurchaseAgreementExercise" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_RepurchaseForForwardSharePurchaseAgreementExerciseShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_PreFundedWarrantsExercise" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_PreFundedWarrantsExerciseShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_PaymentForSeriesAPreferredStockSubscribed" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_PaymentForSubSeriesAPreferredStockSubscribed" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="32" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_PaymentForCommonStockSubscribed" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="33" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="34" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="35" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_IssuanceOfCommonStockForAccruedExpensesInConnectionWithTheBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="36" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_StockIssuedDuringPeriodShareNewIssuanceOfSeriesAPreferredStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="37" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="38" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfCashFlows">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromConvertibleDebt" xlink:label="us-gaap_ProceedsFromConvertibleDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="us-gaap_TypeAndTierIdentifierDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" xlink:label="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantsMember" xlink:label="revb_RolloverWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_DeferredOfferingCostsIncludedInAccountsPayableAndAccruedExpenses" xlink:label="revb_DeferredOfferingCostsIncludedInAccountsPayableAndAccruedExpenses"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:label="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="us-gaap_TypeAndTierIdentifierDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfConvertibleDebt" xlink:label="us-gaap_RepaymentsOfConvertibleDebt"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SeriesA1PreferredStockMember" xlink:label="revb_SeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsMember" xlink:label="revb_PreFundedWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation" xlink:label="us-gaap_Depreciation"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashOrPartNonCashAcquisitionCurrentLiabilitiesAssumed" xlink:label="revb_NoncashOrPartNonCashAcquisitionCurrentLiabilitiesAssumed"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IncreaseDecreaseInDeferredOfferingCosts" xlink:label="revb_IncreaseDecreaseInDeferredOfferingCosts"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromBusinessCombinationFinancingActivity" xlink:label="revb_ProceedsFromBusinessCombinationFinancingActivity"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NonCashLeaseExpense" xlink:label="revb_NonCashLeaseExpense"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_DeferredUnderwritingCommissionsAssumedInBusinessCombination" xlink:label="revb_DeferredUnderwritingCommissionsAssumedInBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromPipeInvestmentFinancingActivity" xlink:label="revb_ProceedsFromPipeInvestmentFinancingActivity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashConversionOfPreferredToCommonStock" xlink:label="revb_NoncashConversionOfPreferredToCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="us-gaap_ProceedsFromWarrantExercises"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashEquityIssuanceForFeesUponBusinessCombination" xlink:label="revb_NoncashEquityIssuanceForFeesUponBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability" xlink:label="us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RepurchaseForTheForwardSharePurchaseAgreementExercise" xlink:label="revb_RepurchaseForTheForwardSharePurchaseAgreementExercise"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashIssuanceOfCommonWarrantsPipeInvestment" xlink:label="revb_NoncashIssuanceOfCommonWarrantsPipeInvestment"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IncreaseDecreaseInAccruedInterestNotesPayableAndConvertibleNote" xlink:label="revb_IncreaseDecreaseInAccruedInterestNotesPayableAndConvertibleNote"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RepaymentsOfNotesPayableIncludingInterest" xlink:label="revb_RepaymentsOfNotesPayableIncludingInterest"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashIssuanceOfPlacementAgentWarrantsWithPipeInvestment" xlink:label="revb_NoncashIssuanceOfPlacementAgentWarrantsWithPipeInvestment"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromPublicOfferingNet" xlink:label="revb_ProceedsFromPublicOfferingNet"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashOrPartNoncashPremiumFinancingAgreement" xlink:label="revb_NoncashOrPartNoncashPremiumFinancingAgreement"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ConversionOfAccruedExpensesToEquityInConnectionWithTheBusinessCombination" xlink:label="revb_ConversionOfAccruedExpensesToEquityInConnectionWithTheBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:label="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashIssuanceOfNewCommonStockWarrantsWithPublicOffering" xlink:label="revb_NoncashIssuanceOfNewCommonStockWarrantsWithPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoncashIssuanceOfNewPlacementAgentWarrantsWithPublicOffering" xlink:label="revb_NoncashIssuanceOfNewPlacementAgentWarrantsWithPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IssuanceOfWarrantsInConnectionWithSeriesA1PreferredStock" xlink:label="revb_IssuanceOfWarrantsInConnectionWithSeriesA1PreferredStock"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromConvertibleDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeAndTierIdentifierDomain" xlink:to="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetIncomeLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_RolloverWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_DeferredOfferingCostsIncludedInAccountsPayableAndAccruedExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:to="us-gaap_TypeAndTierIdentifierDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:to="us-gaap_TypeAndTierIdentifierDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfConvertibleDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PreFundedWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_Depreciation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashOrPartNonCashAcquisitionCurrentLiabilitiesAssumed" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="revb_IncreaseDecreaseInDeferredOfferingCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="revb_ProceedsFromBusinessCombinationFinancingActivity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="revb_NonCashLeaseExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_DeferredUnderwritingCommissionsAssumedInBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="revb_ProceedsFromPipeInvestmentFinancingActivity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashConversionOfPreferredToCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromWarrantExercises" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashEquityIssuanceForFeesUponBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingLeaseLiability" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="revb_RepurchaseForTheForwardSharePurchaseAgreementExercise" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashIssuanceOfCommonWarrantsPipeInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="revb_IncreaseDecreaseInAccruedInterestNotesPayableAndConvertibleNote" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="revb_RepaymentsOfNotesPayableIncludingInterest" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashIssuanceOfPlacementAgentWarrantsWithPipeInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="revb_ProceedsFromPublicOfferingNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashOrPartNoncashPremiumFinancingAgreement" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_ConversionOfAccruedExpensesToEquityInConnectionWithTheBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashIssuanceOfNewCommonStockWarrantsWithPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_NoncashIssuanceOfNewPlacementAgentWarrantsWithPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="revb_IssuanceOfWarrantsInConnectionWithSeriesA1PreferredStock" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsTables">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="us-gaap_ClassOfWarrantOrRightTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantsMember" xlink:label="revb_RolloverWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassACommonStockWarrantsMember" xlink:label="revb_ClassACommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassAPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassAPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBCommonStockWarrantsMember" xlink:label="revb_ClassBCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassBPlacementAgentCommonStockWarrantsMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_RolloverWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassACommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassAPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureOrganizationAndBasisOfPresentationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_BusinessCombinationMember" xlink:label="revb_BusinessCombinationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_UnitsSeparatedIntoCommonStockAndPublicWarrantDescription" xlink:label="revb_UnitsSeparatedIntoCommonStockAndPublicWarrantDescription"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="us-gaap_ConversionOfStockSharesIssued1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_BusinessAcquisitionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_IPOMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_BusinessCombinationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="revb_UnitsSeparatedIntoCommonStockAndPublicWarrantDescription" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_SubsequentEventTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ConversionOfStockSharesIssued1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ConversionOfStockSharesConverted1" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureBusinessCombinationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraShareRepurchaseMember" xlink:label="revb_PetraShareRepurchaseMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_BusinessCombinationMember" xlink:label="revb_BusinessCombinationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraMember" xlink:label="revb_PetraMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraCommonStockMember" xlink:label="revb_PetraCommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementAxis" xlink:label="revb_AgreementAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementDomain" xlink:label="revb_AgreementDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementDomain" xlink:label="revb_AgreementDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ForwardSharePurchaseAgreementMember" xlink:label="revb_ForwardSharePurchaseAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateSharesOfCommonStock" xlink:label="revb_AggregateSharesOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraAcquisitionIncMember" xlink:label="revb_PetraAcquisitionIncMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonUnitAuthorized" xlink:label="us-gaap_CommonUnitAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockConvertibleConversionPriceIncrease" xlink:label="us-gaap_CommonStockConvertibleConversionPriceIncrease"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonUnitIssued" xlink:label="us-gaap_CommonUnitIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonUnitOutstanding" xlink:label="us-gaap_CommonUnitOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssued" xlink:label="us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockOptionExercisePriceIncrease" xlink:label="us-gaap_StockOptionExercisePriceIncrease"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_EscrowedAmount" xlink:label="revb_EscrowedAmount"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ReleasedAmount" xlink:label="revb_ReleasedAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SharesAmountRepurchasedEscrowedAndReturned" xlink:label="revb_SharesAmountRepurchasedEscrowedAndReturned"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregatePurchasePrice" xlink:label="revb_AggregatePurchasePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockNoParValue" xlink:label="us-gaap_CommonStockNoParValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodValue" xlink:label="us-gaap_StockRedeemedOrCalledDuringPeriodValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodShares" xlink:label="us-gaap_StockRedeemedOrCalledDuringPeriodShares"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="us-gaap_OtherIntangibleAssetsNet"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_BusinessCombinationSharesIssued" xlink:label="revb_BusinessCombinationSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAnnualPrincipalPayment" xlink:label="us-gaap_DebtInstrumentAnnualPrincipalPayment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentIncreaseAccruedInterest" xlink:label="us-gaap_DebtInstrumentIncreaseAccruedInterest"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RepaymentsOfNotesPayableIncludingInterestExpenses" xlink:label="revb_RepaymentsOfNotesPayableIncludingInterestExpenses"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PlanNameDomain" xlink:to="revb_PetraShareRepurchaseMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_BusinessCombinationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="revb_PetraMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_PetraCommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="revb_AgreementAxis" xlink:to="revb_AgreementDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="revb_AgreementAxis" xlink:to="revb_AgreementDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_AgreementDomain" xlink:to="revb_ForwardSharePurchaseAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_AggregateSharesOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_PetraAcquisitionIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonUnitAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockConvertibleConversionPriceIncrease" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="revb_AgreementAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_PlanNameAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonUnitIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonUnitOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_EquityMethodInvestmentOwnershipPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_SharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_StockOptionExercisePriceIncrease" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_EscrowedAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_ReleasedAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_SharesAmountRepurchasedEscrowedAndReturned" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_AggregatePurchasePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockNoParValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_StockRedeemedOrCalledDuringPeriodValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_StockRedeemedOrCalledDuringPeriodShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_Goodwill" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_OtherIntangibleAssetsNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_BusinessCombinationSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentAnnualPrincipalPayment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentIncreaseAccruedInterest" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="revb_RepaymentsOfNotesPayableIncludingInterestExpenses" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureBalanceSheetDetailsScheduleOfAccruedExpensesDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:label="srt_CondensedBalanceSheetStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedBalanceSheetStatementTable" xlink:label="srt_CondensedBalanceSheetStatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="us-gaap_TypeAndTierIdentifierDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" xlink:label="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:label="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AccruedClinicalStudyExpenses" xlink:label="revb_AccruedClinicalStudyExpenses"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent" xlink:label="us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AccruedClinicalDevelopmentCosts" xlink:label="revb_AccruedClinicalDevelopmentCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PremiumFinanceAgreement" xlink:label="revb_PremiumFinanceAgreement"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesCurrentAndNoncurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="srt_CondensedBalanceSheetStatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeAndTierIdentifierDomain" xlink:to="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="srt_CondensedBalanceSheetStatementTable" xlink:to="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:to="us-gaap_TypeAndTierIdentifierDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="revb_AccruedClinicalStudyExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="revb_AccruedClinicalDevelopmentCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="revb_PremiumFinanceAgreement" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/revb_r_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommitmentsandContingenciesDetailsLineItems" xlink:label="revb_CommitmentsandContingenciesDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommitmentsandContingenciesDetailsTable" xlink:label="revb_CommitmentsandContingenciesDetailsTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeAndTierIdentifierDomain" xlink:label="us-gaap_TypeAndTierIdentifierDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" xlink:label="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PremiumFinanceAgreementMember" xlink:label="revb_PremiumFinanceAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseContractualTermDomain" xlink:label="us-gaap_LeaseContractualTermDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_OriginalLeaseMember" xlink:label="revb_OriginalLeaseMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseContractualTermAxis" xlink:label="us-gaap_LeaseContractualTermAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraCommonStockMember" xlink:label="revb_PetraCommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="us-gaap_LongtermDebtTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="us-gaap_LongtermDebtTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="us-gaap_LongtermDebtTypeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseContractualTermDomain" xlink:label="us-gaap_LeaseContractualTermDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LandSubjectToGroundLeases" xlink:label="us-gaap_LandSubjectToGroundLeases"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:label="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleDebtMember" xlink:label="us-gaap_ConvertibleDebtMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_FirstAmendmentMember" xlink:label="revb_FirstAmendmentMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseOptionToExtend" xlink:label="us-gaap_LesseeOperatingLeaseOptionToExtend"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" xlink:label="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseExpirationDate1" xlink:label="us-gaap_LeaseExpirationDate1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecurityDepositLiability" xlink:label="us-gaap_SecurityDepositLiability"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseExpense" xlink:label="us-gaap_OperatingLeaseExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodShares" xlink:label="us-gaap_StockRedeemedOrCalledDuringPeriodShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommonStockTransferred" xlink:label="revb_CommonStockTransferred"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_InterestIncurred" xlink:label="revb_InterestIncurred"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentPeriodicPaymentInterest" xlink:label="us-gaap_DebtInstrumentPeriodicPaymentInterest"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentPeriodicPayment" xlink:label="us-gaap_DebtInstrumentPeriodicPayment"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfMonthlyInstallments" xlink:label="revb_NumberOfMonthlyInstallments"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFrequencyOfPeriodicPayment" xlink:label="us-gaap_DebtInstrumentFrequencyOfPeriodicPayment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="us-gaap_DebtInstrumentMaturityDate"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_UpfrontPaymentDue" xlink:label="revb_UpfrontPaymentDue"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ExpenseIncurredForUpfrontMonthlyAndInterestPayments" xlink:label="revb_ExpenseIncurredForUpfrontMonthlyAndInterestPayments"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CashPaidForUpfrontMonthlyAndInterestPaymentsUnderFinanceAgreement" xlink:label="revb_CashPaidForUpfrontMonthlyAndInterestPaymentsUnderFinanceAgreement"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractualObligation" xlink:label="us-gaap_ContractualObligation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRepurchaseOfInitialPublicOffering" xlink:label="us-gaap_PaymentsForRepurchaseOfInitialPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NoninterestExpenseInvestmentAdvisoryFees" xlink:label="us-gaap_NoninterestExpenseInvestmentAdvisoryFees"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NoninterestExpenseInvestmentAdvisoryFeesInFormOfEquity" xlink:label="revb_NoninterestExpenseInvestmentAdvisoryFeesInFormOfEquity"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TransactionExpenses" xlink:label="revb_TransactionExpenses"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_DeferredUnderwritingFees" xlink:label="revb_DeferredUnderwritingFees"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractualObligationDueInNextTwelveMonths" xlink:label="us-gaap_ContractualObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_CommitmentsandContingenciesDetailsTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeAndTierIdentifierDomain" xlink:to="us-gaap_DirectorsAndOfficersLiabilityInsuranceMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_PremiumFinanceAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LeaseContractualTermDomain" xlink:to="revb_OriginalLeaseMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="us-gaap_LeaseContractualTermAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_PetraCommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LeaseContractualTermAxis" xlink:to="us-gaap_LeaseContractualTermDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LeaseContractualTermAxis" xlink:to="us-gaap_LeaseContractualTermDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LandSubjectToGroundLeases" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" xlink:to="us-gaap_TypeAndTierIdentifierDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongtermDebtTypeDomain" xlink:to="us-gaap_ConvertibleDebtMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LeaseContractualTermDomain" xlink:to="revb_FirstAmendmentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LesseeOperatingLeaseTermOfContract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="us-gaap_LongtermDebtTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LesseeOperatingLeaseOptionToExtend" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="us-gaap_BusinessAcquisitionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LeaseExpirationDate1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_CommitmentsandContingenciesDetailsTable" xlink:to="us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_SecurityDepositLiability" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_OperatingLeaseExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentFaceAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_StockRedeemedOrCalledDuringPeriodShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_CommonStockTransferred" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_InterestIncurred" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentPeriodicPaymentInterest" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentPeriodicPayment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_NumberOfMonthlyInstallments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentFrequencyOfPeriodicPayment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_DebtInstrumentMaturityDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_UpfrontPaymentDue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_ExpenseIncurredForUpfrontMonthlyAndInterestPayments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_CashPaidForUpfrontMonthlyAndInterestPaymentsUnderFinanceAgreement" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_ContractualObligation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_PaymentsForRepurchaseOfInitialPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_NoninterestExpenseInvestmentAdvisoryFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_NoninterestExpenseInvestmentAdvisoryFeesInFormOfEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_TransactionExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="revb_DeferredUnderwritingFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_AccruedLiabilitiesCurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_CommitmentsandContingenciesDetailsLineItems" xlink:to="us-gaap_ContractualObligationDueInNextTwelveMonths" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePipeInvestmentDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:label="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PlacementAgentMember" xlink:label="revb_PlacementAgentMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementAxis" xlink:label="revb_AgreementAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementDomain" xlink:label="revb_AgreementDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SecuritiesPurchaseAgreementMember" xlink:label="revb_SecuritiesPurchaseAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsMember" xlink:label="revb_PreFundedWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrivatePlacementMember" xlink:label="us-gaap_PrivatePlacementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassACommonStockWarrantsMember" xlink:label="revb_ClassACommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_GrossPurchasePrice" xlink:label="revb_GrossPurchasePrice"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommonWarrantsMember" xlink:label="revb_CommonWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ProceedsFromPipeInvestmentNetIssuanceCosts" xlink:label="revb_ProceedsFromPipeInvestmentNetIssuanceCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ExceedsPercentage" xlink:label="revb_ExceedsPercentage"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CashFeePercentage" xlink:label="revb_CashFeePercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_OutstandingCommonStockPercentage" xlink:label="revb_OutstandingCommonStockPercentage"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PurchasePrice" xlink:label="revb_PurchasePrice"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="revb_PlacementAgentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="revb_AgreementAxis" xlink:to="revb_AgreementDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_AgreementDomain" xlink:to="revb_SecuritiesPurchaseAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PreFundedWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="revb_AgreementAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_PrivatePlacementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassACommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_GrossPurchasePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_CommonWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_ProceedsFromPipeInvestmentNetIssuanceCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_WarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_ExceedsPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_CashFeePercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_OutstandingCommonStockPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="revb_PurchasePrice" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePublicOfferingDetails">
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicOfferingLineItems" xlink:label="revb_PublicOfferingLineItems"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicOfferingTable" xlink:label="revb_PublicOfferingTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NewCommonStockWarrantMember" xlink:label="revb_NewCommonStockWarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PlacementAgentWarrantsMember" xlink:label="revb_PlacementAgentWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBCommonStockWarrantsMember" xlink:label="revb_ClassBCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived" xlink:label="revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassBPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PlacementAgentCashFeeAmount" xlink:label="revb_PlacementAgentCashFeeAmount"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_WarrantsAndRightsExpirationPeriod" xlink:label="revb_WarrantsAndRightsExpirationPeriod"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateNumberOfSharesSoldPercentage" xlink:label="revb_AggregateNumberOfSharesSoldPercentage"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassOfWarrantOrRightIssued" xlink:label="revb_ClassOfWarrantOrRightIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateValueOfWarrants" xlink:label="revb_AggregateValueOfWarrants"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_PublicOfferingTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_PublicOfferingTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_NewCommonStockWarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PlacementAgentWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_PlacementAgentCashFeeAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_WarrantsAndRightsExpirationPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_AggregateNumberOfSharesSoldPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_ClassOfWarrantOrRightIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_AggregateValueOfWarrants" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosurePreferredStockDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="us-gaap_ScheduleOfStockByClassTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SeriesA1PreferredStockMember" xlink:label="revb_SeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="us-gaap_ConversionOfStockSharesIssued1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" xlink:label="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockVotingRights" xlink:label="us-gaap_PreferredStockVotingRights"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreferredStockExchangedToCommonStockConnectionWithBusinessCombination" xlink:label="revb_PreferredStockExchangedToCommonStockConnectionWithBusinessCombination"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockLiquidationPreferenceValue" xlink:label="us-gaap_PreferredStockLiquidationPreferenceValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockRedemptionAmount" xlink:label="us-gaap_PreferredStockRedemptionAmount"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ScheduleOfStockByClassTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ConversionOfStockSharesIssued1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockVotingRights" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_PreferredStockExchangedToCommonStockConnectionWithBusinessCombination" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockLiquidationPreferenceValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_PreferredStockRedemptionAmount" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureUnitsDetails">
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicOfferingLineItems" xlink:label="revb_PublicOfferingLineItems"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicOfferingTable" xlink:label="revb_PublicOfferingTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassOfWarrantOrRightForIssuingDescription" xlink:label="revb_ClassOfWarrantOrRightForIssuingDescription"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicWarrantsOutstanding" xlink:label="revb_PublicWarrantsOutstanding"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_PublicOfferingTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_IPOMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="us-gaap_SharePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="revb_PublicOfferingTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_ClassOfWarrantOrRightForIssuingDescription" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_PublicOfferingLineItems" xlink:to="revb_PublicWarrantsOutstanding" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureCommonStockDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="us-gaap_ScheduleOfStockByClassTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_July2022PublicOfferingMember" xlink:label="revb_July2022PublicOfferingMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_BusinessCombinationMember" xlink:label="revb_BusinessCombinationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommonStockIssuanceMember" xlink:label="revb_CommonStockIssuanceMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementAxis" xlink:label="revb_AgreementAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AgreementDomain" xlink:label="revb_AgreementDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SecuritiesPurchaseAgreementMember" xlink:label="revb_SecuritiesPurchaseAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PetraAcquisitionIncMember" xlink:label="revb_PetraAcquisitionIncMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ForwardSharePurchaseAgreementMember" xlink:label="revb_ForwardSharePurchaseAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsMember" xlink:label="revb_PreFundedWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_CommonWarrantsMember" xlink:label="revb_CommonWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityReverseStockSplit" xlink:label="us-gaap_StockholdersEquityReverseStockSplit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateSharesOfCommonStock" xlink:label="revb_AggregateSharesOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromPreviousAcquisition" xlink:label="us-gaap_ProceedsFromPreviousAcquisition"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_EscrowedAmount" xlink:label="revb_EscrowedAmount"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ReleasedAmount" xlink:label="revb_ReleasedAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PurchasePrice" xlink:label="revb_PurchasePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SharesAmountRepurchasedEscrowedAndReturned" xlink:label="revb_SharesAmountRepurchasedEscrowedAndReturned"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="us-gaap_WarrantsAndRightsOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DividendsCommonStockCash" xlink:label="us-gaap_DividendsCommonStockCash"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ScheduleOfStockByClassTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="revb_July2022PublicOfferingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_BusinessCombinationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_CommonStockIssuanceMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="revb_AgreementAxis" xlink:to="revb_AgreementDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_AgreementDomain" xlink:to="revb_SecuritiesPurchaseAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_BusinessAcquisitionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="revb_PetraAcquisitionIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="revb_AgreementDomain" xlink:to="revb_ForwardSharePurchaseAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PreFundedWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="revb_AgreementAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_CommonWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_WarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockholdersEquityReverseStockSplit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_AggregateSharesOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ProceedsFromPreviousAcquisition" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_SubsequentEventTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_EscrowedAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_ReleasedAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_PurchasePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="revb_SharesAmountRepurchasedEscrowedAndReturned" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_WarrantsAndRightsOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_DividendsCommonStockCash" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureCommonStockSummaryOfTotalSharesOfCommonStockReservedForIssuanceDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="us-gaap_ScheduleOfStockByClassTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesAPreferredStockMember" xlink:label="us-gaap_SeriesAPreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_UnvestedUnissuedRolloverRsuAwardsMember" xlink:label="revb_UnvestedUnissuedRolloverRsuAwardsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicWarrantsMember" xlink:label="revb_PublicWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SeriesA1PreferredStockMember" xlink:label="revb_SeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassACommonStockWarrantsMember" xlink:label="revb_ClassACommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_DilutiveSharesMember" xlink:label="revb_DilutiveSharesMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassAPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassAPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockGrantsUnderTwoThousandTwentyOneEquityPlanMember" xlink:label="revb_StockGrantsUnderTwoThousandTwentyOneEquityPlanMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBCommonStockWarrantsMember" xlink:label="revb_ClassBCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassBPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantsMember" xlink:label="revb_RolloverWarrantsMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ScheduleOfStockByClassTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_SeriesAPreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_UnvestedUnissuedRolloverRsuAwardsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PublicWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassACommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_DilutiveSharesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassAPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_StockGrantsUnderTwoThousandTwentyOneEquityPlanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_RolloverWarrantsMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TwoThousandAndTwentyEquityIncentivePlanMember" xlink:label="revb_TwoThousandAndTwentyEquityIncentivePlanMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ScenarioOneMember" xlink:label="revb_ScenarioOneMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingAxis" xlink:label="us-gaap_VestingAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain" xlink:label="us-gaap_VestingDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain" xlink:label="us-gaap_VestingDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_IncentiveStockOptionsMember" xlink:label="revb_IncentiveStockOptionsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_BoardOfDirectorsChairmanMember" xlink:label="srt_BoardOfDirectorsChairmanMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TwoThousandAndTwentyOneEquityIncentivePlanMember" xlink:label="revb_TwoThousandAndTwentyOneEquityIncentivePlanMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ScenarioTwoMember" xlink:label="revb_ScenarioTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PercentageOfAggregateNumberOfOutstandingSharesOfCommonStock" xlink:label="revb_PercentageOfAggregateNumberOfOutstandingSharesOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_OfficersEmployeesAndConsultantsMember" xlink:label="revb_OfficersEmployeesAndConsultantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TimeBasedRestrictedStockUnitsMember" xlink:label="revb_TimeBasedRestrictedStockUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_EquityAwardsMember" xlink:label="revb_EquityAwardsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverRestrictedStockUnitsMember" xlink:label="revb_RolloverRestrictedStockUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_StockOptionsMaximumTerm" xlink:label="revb_StockOptionsMaximumTerm"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfEmployees" xlink:label="revb_NumberOfEmployees"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_WeightedAverageBlackScholesValuePerStockOption" xlink:label="revb_WeightedAverageBlackScholesValuePerStockOption"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PlanNameDomain" xlink:to="revb_TwoThousandAndTwentyEquityIncentivePlanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="revb_ScenarioOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_IncentiveStockOptionsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="srt_BoardOfDirectorsChairmanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PlanNameDomain" xlink:to="revb_TwoThousandAndTwentyOneEquityIncentivePlanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="revb_ScenarioTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="revb_PercentageOfAggregateNumberOfOutstandingSharesOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="revb_OfficersEmployeesAndConsultantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_TimeBasedRestrictedStockUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_TitleOfIndividualAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_StatementScenarioAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_EquityAwardsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_SubsequentEventTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="revb_RolloverRestrictedStockUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_VestingAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="revb_StockOptionsMaximumTerm" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="revb_NumberOfEmployees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="revb_WeightedAverageBlackScholesValuePerStockOption" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationScheduleOfStockOptionsActivityDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationAssumptionsUsedInEstimatingFairValueOfStockOptionsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureStockbasedCompensationSummaryOfStockbasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="us-gaap_IncomeStatementLocationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_GeneralAndAdministrativeExpenseMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_ResearchAndDevelopmentExpenseMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="us-gaap_ClassOfWarrantOrRightTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassOfWarrantOrRightIssued" xlink:label="revb_ClassOfWarrantOrRightIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SubSeriesA1PreferredStockMember" xlink:label="revb_SubSeriesA1PreferredStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantsMember" xlink:label="revb_RolloverWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateSharesOfCommonStock" xlink:label="revb_AggregateSharesOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassACommonStockWarrantsMember" xlink:label="revb_ClassACommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantsAndRightsOutstandingMaturityDate" xlink:label="us-gaap_WarrantsAndRightsOutstandingMaturityDate"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassAPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassAPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfWarrants" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsMember" xlink:label="revb_PreFundedWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="us-gaap_ConversionOfStockSharesIssued1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicWarrantsMember" xlink:label="revb_PublicWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBCommonStockWarrantsMember" xlink:label="revb_ClassBCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PurchasePrice" xlink:label="revb_PurchasePrice"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassBPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_IPOMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="revb_ClassOfWarrantOrRightIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="revb_SubSeriesA1PreferredStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_RolloverWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="revb_AggregateSharesOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassACommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_WarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_WarrantsAndRightsOutstandingMaturityDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassAPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfWarrants" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PreFundedWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ConversionOfStockSharesIssued1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PublicWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="revb_PurchasePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_SaleOfStockPricePerShare" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureWarrantsScheduleOfFairValueOfWarrantsEstimatedUsingBlackscholesOptionPricingModelDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="us-gaap_ClassOfWarrantOrRightTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_RolloverWarrantsMember" xlink:label="revb_RolloverWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassACommonStockWarrantsMember" xlink:label="revb_ClassACommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassAPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassAPlacementAgentCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBCommonStockWarrantsMember" xlink:label="revb_ClassBCommonStockWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassBPlacementAgentCommonStockWarrantsMember" xlink:label="revb_ClassBPlacementAgentCommonStockWarrantsMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_RolloverWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassACommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassAPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBCommonStockWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassBPlacementAgentCommonStockWarrantsMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/revb_r_IncomeTaxesDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwardsLineItems" xlink:label="us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwardsTable" xlink:label="us-gaap_OperatingLossCarryforwardsTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="us-gaap_IncomeTaxAuthorityAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DomesticCountryMember" xlink:label="us-gaap_DomesticCountryMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="us-gaap_TaxCreditCarryforwardAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchMember" xlink:label="us-gaap_ResearchMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="us-gaap_StateAndLocalJurisdictionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="us-gaap_OperatingLossCarryforwards"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NetOperatingLossCarryforwardsExpirationYear" xlink:label="revb_NetOperatingLossCarryforwardsExpirationYear"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="us-gaap_TaxCreditCarryforwardAmount"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TaxCreditCarryforwardsExpirationYear" xlink:label="revb_TaxCreditCarryforwardsExpirationYear"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="us-gaap_UnrecognizedTaxBenefits"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_TaxCutsAndJobsActOf2017LimitationOfNetOperatingLossDeductionsAsPercentageOfTaxableIncome" xlink:label="revb_TaxCutsAndJobsActOf2017LimitationOfNetOperatingLossDeductionsAsPercentageOfTaxableIncome"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued" xlink:label="us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_OperatingLossCarryforwardsTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OperatingLossCarryforwardsTable" xlink:to="us-gaap_IncomeTaxAuthorityAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_DomesticCountryMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_DeferredTaxAssetsValuationAllowance" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_TaxCreditCarryforwardAxis" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_TaxCreditCarryforwardAxis" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardNameDomain" xlink:to="us-gaap_ResearchMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_OperatingLossCarryforwardsTable" xlink:to="us-gaap_TaxCreditCarryforwardAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_StateAndLocalJurisdictionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_OperatingLossCarryforwards" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="revb_NetOperatingLossCarryforwardsExpirationYear" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_TaxCreditCarryforwardAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="revb_TaxCreditCarryforwardsExpirationYear" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_UnrecognizedTaxBenefits" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="revb_TaxCutsAndJobsActOf2017LimitationOfNetOperatingLossDeductionsAsPercentageOfTaxableIncome" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingLossCarryforwardsLineItems" xlink:to="us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://revbiosciences.com/20221231/taxonomy/role/DisclosureSubsequentEventsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventLineItems" xlink:label="us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTable" xlink:label="us-gaap_SubsequentEventTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseContractualTermDomain" xlink:label="us-gaap_LeaseContractualTermDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_FirstAmendmentMember" xlink:label="revb_FirstAmendmentMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NewCommonStockWarrantMember" xlink:label="revb_NewCommonStockWarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseContractualTermAxis" xlink:label="us-gaap_LeaseContractualTermAxis"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_SecondAmendmentMember" xlink:label="revb_SecondAmendmentMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfUnitsSeperation" xlink:label="revb_NumberOfUnitsSeperation"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PublicWarrantsMember" xlink:label="revb_PublicWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfNewSharesIssued" xlink:label="revb_NumberOfNewSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PreFundedWarrantsMember" xlink:label="revb_PreFundedWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassCCommonStockPurchaseWarrantsMember" xlink:label="revb_ClassCCommonStockPurchaseWarrantsMember"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassOfWarrantOrRightIssued" xlink:label="revb_ClassOfWarrantOrRightIssued"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_ClassCCommonStockWarrantMember" xlink:label="revb_ClassCCommonStockWarrantMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_WarrantsAndRightsExpirationPeriod" xlink:label="revb_WarrantsAndRightsExpirationPeriod"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_GrossProceedsFromIssuanceOfPublicOffering" xlink:label="revb_GrossProceedsFromIssuanceOfPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredOfferingCosts" xlink:label="us-gaap_DeferredOfferingCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived" xlink:label="revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PlacementAgentCashFeeAmount" xlink:label="revb_PlacementAgentCashFeeAmount"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_AggregateValueOfWarrants" xlink:label="revb_AggregateValueOfWarrants"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseExpirationDate1" xlink:label="us-gaap_LeaseExpirationDate1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_LesseeOperatingLeaseLiabilityBaseMonthlyRent" xlink:label="revb_LesseeOperatingLeaseLiabilityBaseMonthlyRent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseAndRentalExpense" xlink:label="us-gaap_LeaseAndRentalExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityReverseStockSplit" xlink:label="us-gaap_StockholdersEquityReverseStockSplit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_BidPriceRequirement" xlink:label="revb_BidPriceRequirement"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfConsecutiveBusinessDays" xlink:label="revb_NumberOfConsecutiveBusinessDays"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_NumberOfConsecutiveTradingDays" xlink:label="revb_NumberOfConsecutiveTradingDays"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:loc xlink:type="locator" xlink:href="revb-20221231.xsd#revb_PurchasePrice" xlink:label="revb_PurchasePrice"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_IPOMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LeaseContractualTermDomain" xlink:to="revb_FirstAmendmentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_NewCommonStockWarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsequentEventTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LeaseContractualTermAxis" xlink:to="us-gaap_LeaseContractualTermDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LeaseContractualTermDomain" xlink:to="revb_SecondAmendmentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_NumberOfUnitsSeperation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PublicWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_NumberOfNewSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_PreFundedWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_LeaseContractualTermAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassCCommonStockPurchaseWarrantsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_SubsequentEventTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_ClassOfWarrantOrRightIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="revb_ClassCCommonStockWarrantMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_WarrantsAndRightsExpirationPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_GrossProceedsFromIssuanceOfPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_DeferredOfferingCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_PercentageOfPlacementAgentCashFeeOnGrossProceedsReceived" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_PlacementAgentCashFeeAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_AggregateValueOfWarrants" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_LeaseExpirationDate1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_LesseeOperatingLeaseLiabilityBaseMonthlyRent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_LeaseAndRentalExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockholdersEquityReverseStockSplit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_BidPriceRequirement" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_NumberOfConsecutiveBusinessDays" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_NumberOfConsecutiveTradingDays" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="revb_PurchasePrice" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="2" use="optional"/>
  </link:definitionLink>
</link:linkbase>
