Lewis & Short

bĭformis, e, adj. [bis-forma], double or two-formed, two-shaped (poet. or in postAug. prose): proles biformis Minotaurus, Verg. A. 6, 25: Scyllae, id. ib. 6, 286; Ov. M. 8, 156: Janus, id. F. 1, 89; 5, 424: (Hermaphroditus), id. M. 4, 387: pater, i. e. Chiron, id. ib. 2, 664: Nessus, id. ib. 9, 121: Hodites, id. ib. 12, 456: monstrum, id. ib. 8, 156: a Centaur, id. Am. 2, 12, 19; Claud. in Rufin. 1, 329 (cf. biformatus): Pan, Col. 10, 427: Glaucus, Claud. Rapt. Pros. 3, 12: Cecrops, Just. 2, 6, 7.
Trop., of a poet (as man and swan): vates, * Hor. C. 2, 20, 3: biformes hominum partus, Tac. A. 12, 64.