<?xml version="1.0" encoding="us-ascii"?>
<!-- XBRL document created with Praxa -->
<!-- Copyright (c) 2026 Praxa LLC. All Rights Reserved.-->
<!-- Creation Date: 2026-10-07T20:20:07.6883+00:00 -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <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:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/SponsorsAffiliateOrPromotersOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#SponsorsAffiliatesOrPromotersOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/SecurityClassesOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#SecurityClassesOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/RedemptionLevelsOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#RedemptionLevelsOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/OverAllotmentOptionsOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#OverAllotmentOptionsOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/DilutionSourcesOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#DilutionSourcesOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/ConflictOfInterestPartiesOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#ConflictOfInterestPartiesOnly" xlink:type="simple" />
  <link:roleRef roleURI="http://xbrl.sec.gov/spac/role/CompensationNaturesOnly" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#CompensationNaturesOnly" xlink:type="simple" />
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/SponsorsAffiliateOrPromotersOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllSpacSponsorsAffiliatesOrPromotersMember" xlink:label="spac_AllSpacSponsorsAffiliatesOrPromotersMember_1072" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_HarbourIslandAcquisitionSponsorLLCMember" xlink:label="ck0002131072_HarbourIslandAcquisitionSponsorLLCMember_45117" />
    <link:definitionArc xlink:type="arc" order="127.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSpacSponsorsAffiliatesOrPromotersMember_1072" xlink:to="ck0002131072_HarbourIslandAcquisitionSponsorLLCMember_45117" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/SecurityClassesOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllSecurityClassesMember" xlink:label="spac_AllSecurityClassesMember_1087" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_LessAmountsPaidForRedemptionsMember" xlink:label="ck0002131072_LessAmountsPaidForRedemptionsMember_45107" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_LessDeferredUnderwritingCommissionsMember" xlink:label="ck0002131072_LessDeferredUnderwritingCommissionsMember_45105" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_LessOrdinarySharesRedeemedMember" xlink:label="ck0002131072_LessOrdinarySharesRedeemedMember_45112" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_LessOverallotmentLiabilityMember" xlink:label="ck0002131072_LessOverallotmentLiabilityMember_45106" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_NetProceedsFromThisOfferingAndTheSaleOfThePlacementSharesMember" xlink:label="ck0002131072_NetProceedsFromThisOfferingAndTheSaleOfThePlacementSharesMember_45103" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_NetTangibleBookDeficitBeforeThisOfferingMember" xlink:label="ck0002131072_NetTangibleBookDeficitBeforeThisOfferingMember_45097" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OrdinarySharesForfeitedIfOverallotmentIsNotExercisedMember" xlink:label="ck0002131072_OrdinarySharesForfeitedIfOverallotmentIsNotExercisedMember_45109" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OrdinarySharesOfferedAndSaleOfPlacementSharesMember" xlink:label="ck0002131072_OrdinarySharesOfferedAndSaleOfPlacementSharesMember_45110" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OrdinarySharesOutstandingPriorToThisOfferingMember" xlink:label="ck0002131072_OrdinarySharesOutstandingPriorToThisOfferingMember_45108" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_RepresentativeSharesMember" xlink:label="ck0002131072_RepresentativeSharesMember_45111" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_PrivatePlacementSharesMember" xlink:label="ck0002131072_PrivatePlacementSharesMember_45113" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_PlusOfferingCostsAccruedForOrPaidInAdvanceExcludedFromTangibleBookValueMember" xlink:label="ck0002131072_PlusOfferingCostsAccruedForOrPaidInAdvanceExcludedFromTangibleBookValueMember_45104" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OtherUnitsAndConvertibleSecuritiesMember" xlink:label="ck0002131072_OtherUnitsAndConvertibleSecuritiesMember_45115" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_PrivatePlacementUnitsMember" xlink:label="ck0002131072_PrivatePlacementUnitsMember_45114" />
    <link:definitionArc xlink:type="arc" order="117.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_LessAmountsPaidForRedemptionsMember_45107" />
    <link:definitionArc xlink:type="arc" order="115.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_LessDeferredUnderwritingCommissionsMember_45105" />
    <link:definitionArc xlink:type="arc" order="122.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_LessOrdinarySharesRedeemedMember_45112" />
    <link:definitionArc xlink:type="arc" order="116.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_LessOverallotmentLiabilityMember_45106" />
    <link:definitionArc xlink:type="arc" order="113.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_NetProceedsFromThisOfferingAndTheSaleOfThePlacementSharesMember_45103" />
    <link:definitionArc xlink:type="arc" order="107.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_NetTangibleBookDeficitBeforeThisOfferingMember_45097" />
    <link:definitionArc xlink:type="arc" order="119.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_OrdinarySharesForfeitedIfOverallotmentIsNotExercisedMember_45109" />
    <link:definitionArc xlink:type="arc" order="120.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_OrdinarySharesOfferedAndSaleOfPlacementSharesMember_45110" />
    <link:definitionArc xlink:type="arc" order="118.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_OrdinarySharesOutstandingPriorToThisOfferingMember_45108" />
    <link:definitionArc xlink:type="arc" order="121.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_RepresentativeSharesMember_45111" />
    <link:definitionArc xlink:type="arc" order="123.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_PrivatePlacementSharesMember_45113" />
    <link:definitionArc xlink:type="arc" order="114.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_PlusOfferingCostsAccruedForOrPaidInAdvanceExcludedFromTangibleBookValueMember_45104" />
    <link:definitionArc xlink:type="arc" order="125.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_OtherUnitsAndConvertibleSecuritiesMember_45115" />
    <link:definitionArc xlink:type="arc" order="124.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllSecurityClassesMember_1087" xlink:to="ck0002131072_PrivatePlacementUnitsMember_45114" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/RedemptionLevelsOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllRedemptionLevelsMember" xlink:label="spac_AllRedemptionLevelsMember_1091" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/OverAllotmentOptionsOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllOverAllotmentOptionsMember" xlink:label="spac_AllOverAllotmentOptionsMember_1057" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/DilutionSourcesOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllDilutionSourcesMember" xlink:label="spac_AllDilutionSourcesMember_1103" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_WithOverAllotmentMember" xlink:label="ck0002131072_WithOverAllotmentMember_45093" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_WithoutOverAllotmentMember" xlink:label="ck0002131072_WithoutOverAllotmentMember_45092" />
    <link:definitionArc xlink:type="arc" order="106.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllDilutionSourcesMember_1103" xlink:to="ck0002131072_WithOverAllotmentMember_45093" />
    <link:definitionArc xlink:type="arc" order="105.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllDilutionSourcesMember_1103" xlink:to="ck0002131072_WithoutOverAllotmentMember_45092" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/ConflictOfInterestPartiesOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllConflictOfInterestPartiesMember" xlink:label="spac_AllConflictOfInterestPartiesMember_45126" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_InitialShareholdersMember" xlink:label="ck0002131072_InitialShareholdersMember_45130" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OurSponsorMember" xlink:label="ck0002131072_OurSponsorMember_45131" />
    <link:definitionArc xlink:type="arc" order="140.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllConflictOfInterestPartiesMember_45126" xlink:to="ck0002131072_InitialShareholdersMember_45130" />
    <link:definitionArc xlink:type="arc" order="141.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllConflictOfInterestPartiesMember_45126" xlink:to="ck0002131072_OurSponsorMember_45131" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/spac/role/CompensationNaturesOnly" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/spac/2026/spac-2026.xsd#spac_AllCompensationNaturesMember" xlink:label="spac_AllCompensationNaturesMember_1074" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_LoanMember" xlink:label="ck0002131072_LoanMember_45121" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_PrivatePlacementUnitsMember" xlink:label="ck0002131072_PrivatePlacementUnitsMember_45120" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_ClassBOrdinarySharesMember" xlink:label="ck0002131072_ClassBOrdinarySharesMember_45119" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_OfficeSpaceAdministrativeAndSharedPersonnelSupportServicesMember" xlink:label="ck0002131072_OfficeSpaceAdministrativeAndSharedPersonnelSupportServicesMember_45118" />
    <link:loc xlink:type="locator" xlink:href="ck0002131072-20260331.xsd#ck0002131072_WorkingCapitalLoansMember" xlink:label="ck0002131072_WorkingCapitalLoansMember_45122" />
    <link:definitionArc xlink:type="arc" order="131.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllCompensationNaturesMember_1074" xlink:to="ck0002131072_LoanMember_45121" />
    <link:definitionArc xlink:type="arc" order="130.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllCompensationNaturesMember_1074" xlink:to="ck0002131072_PrivatePlacementUnitsMember_45120" />
    <link:definitionArc xlink:type="arc" order="129.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllCompensationNaturesMember_1074" xlink:to="ck0002131072_ClassBOrdinarySharesMember_45119" />
    <link:definitionArc xlink:type="arc" order="128.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllCompensationNaturesMember_1074" xlink:to="ck0002131072_OfficeSpaceAdministrativeAndSharedPersonnelSupportServicesMember_45118" />
    <link:definitionArc xlink:type="arc" order="132.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="spac_AllCompensationNaturesMember_1074" xlink:to="ck0002131072_WorkingCapitalLoansMember_45122" />
  </link:definitionLink>
</link:linkbase>
