The Collaborative International Dictionary of English v.0.48:

Metamorphic \Met`a*mor"phic\, a. [See Metamorphosis.]
   1. Subject to change; changeable; variable.
      [1913 Webster]

   2. Causing a change of structure.
      [1913 Webster]

   3. (Geol.) Pertaining to, produced by, or exhibiting, certain
      changes which minerals or rocks may have undergone since
      their original deposition; -- especially applied to the
      recrystallization which sedimentary rocks have undergone
      through the influence of heat and pressure, after which
      they are called metamorphic rocks.
      [1913 Webster]

WordNet (r) 3.0 (2006):

metamorphic
    adj 1: of or relating to metamorphosis (especially of rocks);
           "metamorphic stage"; "marble is a metamorphic rock that
           takes a high polish" [syn: metamorphic, metamorphous]
    2: characterized by metamorphosis or change in physical form or
       substance [ant: nonmetamorphic]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "metamorphic":
   able to adapt, adaptable, adjustable, allotropic, alterable,
   alterative, anabolic, catabolic, catalytic, changeable, checkered,
   diversiform, ever-changing, flexible, fluid, heteromorphic,
   heteromorphous, impermanent, kaleidoscopic, malleable, manifold,
   many-sided, metabolic, metamorphotic, metastatic, mobile,
   modifiable, movable, multifarious, multifold, multiform,
   multiphase, multiple, multiplex, mutable, nonuniform, permutable,
   plastic, polymorphic, polymorphous, protean, proteiform, resilient,
   rubbery, supple, transient, transitory, variable