The Collaborative International Dictionary of English v.0.48:
Bipinnate \Bi*pin"nate\, Bipinnated \Bi*pin"na*ted\, a. [Pref. bi- + pinnate; cf. F. bipinn['e]. Cf. Bipennate.] Twice pinnate. [1913 Webster]WordNet (r) 3.0 (2006):
bipinnate adj 1: of a leaf shape; having doubly pinnate leaflets (as ferns)