guarantee n[probably alteration of guaranty ]
1 : guarantor
2 : guaranty
3 : an assurance that a condition will be fulfilled: as
a : an agreement by which one person undertakes to secure another in the possession or enjoyment of something
b : an assurance of the quality or of the length of use to be expected from a product offered for sale often with a promise of reimbursement
4 : guaranty [constitutional s ]
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.