Guarantee  —n. 1 a formal promise or assurance, esp. That something is of a specified quality and durability. B document giving such an undertaking. 2 = *guaranty. 3 person making a guaranty or giving a security. —v. (-tees, -teed) 1 a give or serve as a guarantee for. B provide with a guarantee. 2 give a promise or assurance. 3 (foll. By to) secure the possession of (a thing) for a person. [related to *warrant]