I. noun
1.
an assurance for the fulfillment of a condition
gave him a guarantee that the work would be done according to specifications
Synonyms: bail, bond, guaranty, security, surety, warranty; compare pledge 1
Related Word: earnest, pledge, promise, token, undertaking, word; oath, vow
2.
Synonyms: word 8, assurance, pledge, warrant
II. verb
Synonyms: warrant 2, certify, guaranty