trifid

from WordNet (r) 3.0 (2006)

trifid
    adj 1: divided into three lobes; "trifid petals"

from 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]