An Etymological Dictionary of Astronomy and Astrophysics

A large, amphibious rodent of the genus Castor, having sharp incisors, webbed hind feet, and a flattened tail, noted for its ability to dam streams with trees, branches, etc. (Dictionary.com).

Etymology (EN): M.E. bever, O.E. beofor, befor; cognate with Ger. Biber; Av. bawra-, bawri- “beaver” (Mid.Pers. bawrak “beaver”);
Skt. babhrav- “reddish-brown,” babhrus- “mangoose,” L. fiber “beaver” (Fr. bièvre “River of Beavers”); O.H.G. biorr; Lith. bêbrus; Rus. bobr “beaver.”

Etymology (PE): Bidastar “beaver,” of unknown origin.