The Collaborative International Dictionary of English v.0.48:

Trifurcate \Tri*fur"cate\, Trifurcated \Tri*fur"ca*ted\, a. [L.
   trifurcus; tri- (see Tri-) + furca fork.]
   Having three branches or forks; trichotomous.
   [1913 Webster]

WordNet (r) 3.0 (2006):

trifurcate
    v 1: divide into three; "The road trifurcates at the bridge"

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "trifurcate":
   V-shaped, Y-shaped, arboreal, arborescent, arboriform, biforked,
   bifurcate, bifurcated, branched, branching, branchlike, crotched,
   deltoid, dendriform, dendritic, forked, forking, forklike, furcate,
   pronged, ramous, three-cornered, three-dimensional, three-footed,
   three-pronged, three-sided, tree-shaped, treelike, triangular,
   triangulate, triarch, trichotomous, tricorn, tricornered,
   tricuspid, trident, tridental, tridentlike, trifid, triflorate,
   triflorous, trifurcated, trigonal, trigonoid, trigrammatic,
   trihedral, trilateral, trimerous, triparted, tripartite, tripodic,
   triquetral, triquetrous, trisected