guarantee

[1]	guaranty , warranty , assure , ensure , pledge , promise , undertake , stand behind , vouch for , certify , make sure/certain , swear to , attest to
[2]	vouch
[3]	ensure , insure , assure , secure
[4]	undertake
[5]	warrant

[1]	guaranty , warrant , warrantee , warranty , assurance , warranty , pledge , bond , obligation , promise , word (of honour) , oath , undertaking
[2]	guaranty