The Collaborative International Dictionary of English v.0.48:

Metabolism \Me*tab"o*lism\, n. (Physiol.)
   1. The act or process, by which living tissues or cells take
      up and convert into their own proper substance the
      nutritive material brought to them by the blood, or by
      which they transform their cell protoplasm into simpler
      substances, which are fitted either for excretion or for
      some special purpose, as in the manufacture of the
      digestive enzymes. Hence, metabolism may be either
      constructive (anabolism), or destructive (catabolism).
      [1913 Webster]

   2. (Biol.) The series of chemical changes which take place in
      an organism, by means of which food is manufactured and
      utilized and waste materials are eliminated.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

metabolism
    n 1: the marked and rapid transformation of a larva into an
         adult that occurs in some animals [syn: metamorphosis,
         metabolism]
    2: the organic processes (in a cell or organism) that are
       necessary for life [syn: metabolism, metabolic process]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "metabolism":
   assimilation, avatar, basal metabolism, catabolism, catalysis,
   consubstantiation, displacement, heterotopia, metagenesis,
   metamorphism, metamorphosis, metastasis, metathesis,
   metempsychosis, mutant, mutated form, mutation, permutation,
   reincarnation, sport, transanimation, transfiguration,
   transfigurement, transformation, transformism, translation,
   translocation, transmigration, transmogrification, transmutation,
   transposition, transubstantiation