The Collaborative International Dictionary of English v.0.48:
Biform \Bi"form\, a. [L. biformis; bis twice + forma shape: cf. F. biforme.] Having two forms, bodies, or shapes. --Croxall. [1913 Webster]WordNet (r) 3.0 (2006):
biform adj 1: having or combining two forms; "a biform crystal"; "the biform body of a mermaid"