Source : Webster's Revised Unabridged Dictionary (1913)

Pleomorphism \Ple`o*mor"phism\, n. [Gr. ? more + ? form.]
   1. (Crystallog.) The property of crystallizing under two or
      more distinct fundamental forms, including dimorphism and
      trimorphism.

   2. (Biol.) The theory that the various genera of bacteria are
      phases or variations of growth of a number of Protean
      species, each of which may exhibit, according to
      undetermined conditions, all or some of the forms
      characteristic of the different genera and species.

Source : WordNet®

pleomorphism
     n 1: (chemistry) the existence of different kinds of crystal of
          the same chemical compound [syn: {polymorphism}]
     2: (biology) the appearance of two or more distinctly different
        forms in the life cycle of some organisms