The Collaborative International Dictionary of English v.0.48:

Amortize \A*mor"tize\, v. t. [OE. amortisen, LL. amortisare,
   admortizare, F. amortir to sell in mortmain, to extinguish;
   L. ad + mors death. See Mortmain].
   1. To make as if dead; to destroy. [Obs.] --Chaucer.
      [1913 Webster]

   2. (Law) To alienate in mortmain, that is, to convey to a
      corporation. See Mortmain.
      [1913 Webster]

   3. To clear off or extinguish, as a debt, usually by means of
      a sinking fund.
      [1913 Webster]

WordNet (r) 3.0 (2006):

amortize
    v 1: liquidate gradually [syn: amortize, amortise]