The Collaborative International Dictionary of English v.0.48:
Tripinnate \Tri*pin"nate\, a. [Pref. tri- + pinnate.] (Bot.) Having bipinnate leaflets arranged on each side of a rhachis. [1913 Webster]WordNet (r) 3.0 (2006):
tripinnate adj 1: (of a leaf shape) thrice pinnate [syn: tripinnate, tripinnated]