The Collaborative International Dictionary of English v.0.48:
Castoroides \Castoroides\ n. a genus of extinct beavers of the Pleistocene; of eastern and southern U.S. Syn: genus Castoroides. [WordNet 1.5]WordNet (r) 3.0 (2006):
Castoroides n 1: extinct beavers of the Pleistocene; of eastern and southern United States [syn: Castoroides, genus Castoroides]