surety
noun | \ ˈshu̇r-ə-tē \ | sure·ty
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: a formal engagement (as a pledge) given for the fulfillment of an undertaking
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: one (as an accommodation party) who promises to answer for the debt or default of another
Note: At common law a surety is distinguished from a guarantor by being immediately liable as opposed to becoming liable only upon default of the principal. Under the Uniform Commercial Code, however, a surety includes a guarantor, and the two terms are generally interchangeable.