The Collaborative International Dictionary of English v.0.48:

Monomorphic \Mon`o*mor"phic\, Monomorphous \Mon`o*mor"phous\, a.
   [Mono- + Gr. morfh` form.] (Biol.)
   Having but a single form; retaining the same form throughout
   the various stages of development; of the same or of an
   essentially similar type of structure; -- opposed to
   dimorphic, trimorphic, and polymorphic.
   [1913 Webster]