Source : Webster's Revised Unabridged Dictionary (1913)

Guaranty \Guar"an*ty\, n.; pl. {Guaranies}. [OF. guarantie,
   garantie, F. garantie, OF. guarantir, garantir, to warrant,
   to guaranty, E. garantir, fr. OF. guarant, garant, a
   warranter, F. garant; of German origin, and from the same
   word as warranty. See {Warrant}, and cf. {Warranty},
   {Guarantee}.]
   In law and common usage: An undertaking to answer for the
   payment of some debt, or the performance of some contract or
   duty, of another, in case of the failure of such other to pay
   or perform; a guarantee; a warranty; a security.

Guaranty \Guar"an*ty\, v. t. [imp. & p. p. {Guarantied}; p. pr.
   & vb. n. {Guarantying}.] [From {Guaranty}, n.]
   In law and common usage: To undertake or engage that another
   person shall perform (what he has stipulated); to undertake
   to be answerable for (the debt or default of another); to
   engage to answer for the performance of (some promise or duty
   by another) in case of a failure by the latter to perform; to
   undertake to secure (something) to another, as in the case of
   a contingency. See {Guarantee}, v. t.

   Note: Guaranty agrees in form with warranty. Both guaranty
         and guarantee are well authorized by legal writers in
         the United States. The prevailing spelling, at least
         for the verb, is guarantee.

Source : WordNet®

guaranty
     n : a collateral agreement to answer for the debt of another in
         case that person defaults [syn: {guarantee}]
     [also: {guarantied}]