The Collaborative International Dictionary of English v.0.48:

Katabolism \Ka*tab"o*lism\, n. [Gr. ? down + ? to throw.]
   (Physiol.)
   Destructive or downward metabolism; regressive metamorphism;
   same as catabolism (now the more common spelling); --
   opposed to anabolism. See Disassimilation.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

catabolism \catabolism\ n.
   the breakdown of more complex substances into simpler ones
   with release of energy, in living organisms; destructive or
   downward metabolism; -- a form of metabolism, opposed to
   anabolism. See also Disassimilation. [Formerly spelled
   katabolism.]

   Syn: katabolism, dissimilation, destructive metabolism.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

katabolism
    n 1: breakdown in living organisms of more complex substances
         into simpler ones together with release of energy [syn:
         catabolism, katabolism, dissimilation, destructive
         metabolism] [ant: anabolism, constructive metabolism]