The Collaborative International Dictionary of English v.0.48:

Polymorphous \Pol`y*mor"phous\, a.
   1. Having, or assuming, a variety of forms, characters, or
      styles; as, a polymorphous author. --De Quincey.
      [1913 Webster]

   2. (Biol.) Having, or occurring in, several distinct forms;
      -- opposed to monomorphic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

polymorphous
    adj 1: relating to the crystallization of a compound in two or
           more different forms; "polymorphous crystallization"
           [syn: polymorphous, polymorphic]
    2: relating to the occurrence of more than one kind of
       individual (independent of sexual differences) in an
       interbreeding population; "a polymorphic species" [syn:
       polymorphic, polymorphous]
    3: having or occurring in several distinct forms; "man is both
       polymorphic and polytypic"; "a polymorphous god" [syn:
       polymorphic, polymorphous]