The Collaborative International Dictionary of English v.0.48:

Trigamous \Trig"a*mous\, a. [L. trigamus a thrice-married man,
   Gr. ? thrice married; ? (see Tri-) + ? marriage: cf. F.
   trigame.] (Bot.)
   Having three sorts of flowers in the same head, -- male,
   female, and hermaphrodite, or perfect, flowers.
   [1913 Webster]