The Collaborative International Dictionary of English v.0.48:
Trifid \Tri"fid\, a. [L. trifidus; tri- (see Tri-) + the root of findere to split: cf. F. trifide.] Cleft to the middle, or slightly beyond the middle, into three parts; three-cleft. [1913 Webster]WordNet (r) 3.0 (2006):
trifid adj 1: divided into three lobes; "trifid petals"