Lewis & Short

1. castor, ŏris, m., = κάστωρ, the castor, beaver; pure Lat. fiber: Castor fiber, Linn.; Plin. 32, 3, 13, § 26; cf. id. 8, 30, 47, § 109; Cic. ap. Isid. Orig. 12, 2, 21; Ov. Nux. 166; acc. castorem, App. M. 1, p. 106, 10: castora, Juv. 12, 34.