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"guarantee" is also used as a crossword clue. If that's what you saw, the answer is often surety (6 letters).
Definitions
promise to do or accomplish
Word origin
From Old French guarantie (perhaps via a later Spanish garante), from the verb guarantir (“to protect, assure, vouch for”), ultimately from Old Frankish *warjand, *warand (“a warrant”), or from guaranty. Doublet of guaranty and warranty.
Used in a sentence
“Can you give me a guarantee that he will be fit for the match?”
“The cooker comes with a five-year guarantee.”
“But God who is the great Guarantee for the Peace , Order , and good behaviour of Mankind”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer2 curated clues
01“promise”9 letters
02“Vouch for”9 letters
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