The Collaborative International Dictionary of English v.0.48:

Metamorphosis \Met`a*mor"pho*sis\, n.; pl. Metamorphoses. [L.,
   fr. Gr. ?, fr. ? to be transformed; meta` beyond, over +
   morfh` form.]
   [1913 Webster]
   1. Change of form, or structure; transformation.
      [1913 Webster]

   2. (Biol.) A change in the form or function of a living
      organism, by a natural process of growth or development;
      as, the metamorphosis of the yolk into the embryo, of a
      tadpole into a frog, or of a bud into a blossom.
      Especially, that form of sexual reproduction in which an
      embryo undergoes a series of marked changes of external
      form, as the chrysalis stage, pupa stage, etc., in
      insects. In these intermediate stages sexual reproduction
      is usually impossible, but they ultimately pass into final
      and sexually developed forms, from the union of which
      organisms are produced which pass through the same cycle
      of changes. See Transformation.
      [1913 Webster]

   3. (Physiol.) The change of material of one kind into another
      through the agency of the living organism; metabolism.
      [1913 Webster]

   Vegetable metamorphosis (Bot.), the doctrine that flowers
      are homologous with leaf buds, and that the floral organs
      are transformed leaves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

metamorphosis
    n 1: the marked and rapid transformation of a larva into an
         adult that occurs in some animals [syn: metamorphosis,
         metabolism]
    2: a striking change in appearance or character or
       circumstances; "the metamorphosis of the old house into
       something new and exciting" [syn: transfiguration,
       metamorphosis]
    3: a complete change of physical form or substance especially as
       by magic or witchcraft

Moby Thesaurus II by Grady Ward, 1.0:

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