a. [ Pref. bi- + form. ] Having two forms. Johnson. [ 1913 Webster ]
n. 1. an order of birds, including the family Podicipedidae, which consitutes the grebes. Syn. -- Podicipitiformes, order Podicipitiformes, Podicipediformes, order Podicipediformes, order Colymbiformes. [ WordNet 1.5 ]