Source : Webster's Revised Unabridged Dictionary (1913)

Katabolism \Ka*tab"o*lism\, n. [Gr. ? down + ? to throw.]
   (Physiol.)
   Destructive or downward metabolism; regressive metamorphism;
   -- opposed to {anabolism}. See {Disassimilation}.

Source : WordNet®

katabolism
     n : breakdown of more complex substances into simpler ones with
         release of energy [syn: {catabolism}, {dissimilation}, {destructive
         metabolism}] [ant: {anabolism}]