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.