Definition of: guarantee

(gar′ən.tē′) noun
1. A pledge or formal assurance that something will meet stated specifications or that a specified act will be performed.
2. Something given as security.
3. A guarantor.
4. Something which assures a certain outcome: Diligence is a guarantee of success.
—v.t. ·teed, ·tee·ing
1. To certify or vouch for the performance of (something); warrant.
2. To make (oneself) responsible for the obligation of another.
3. To secure against loss or damage.
4. To affirm with certainty; promise; swear: He guarantees to be there. [Var. of GUARANTY]