Source : Webster's Revised Unabridged Dictionary (1913)

Polymorph \Pol"y*morph\, n. [Gr. ? multiform; poly`s many + ?
   form: cf. F. polymorphe.] (Crystallog.)
   A substance capable of crystallizing in several distinct
   forms; also, any one of these forms. Cf. {Allomorph}.

Source : WordNet®

polymorph
     n : an organism that can assume more than one adult form as in
         the castes of ants or termites