The Collaborative International Dictionary of English v.0.48:

Triform \Tri"form\, a. [L. triformis; tri- (see Tri-) + forma
   form.]
   Having a triple form or character. "This triform antagonism."
   --I. Taylor.
   [1913 Webster]

         Goddess Triform, I own thy triple spell. --Lowell.
   [1913 Webster]