walrus n.

"large pinniped carnivorous mammal" (the males are noted for their  enormous tusk-like canine teeth), 1650s, from Dutch walrus, which was probably a folk-etymology alteration (by influence of Dutch walvis "whale" and ros "horse") of a Scandinavian word, such as Old Norse rosmhvalr "walrus," hrosshvalr "a kind of whale," or rostungr "walrus." Old English had horschwæl, and later morse, from Lapp morsa or Finnish mursu, which ultimately might be the source, much garbled, of the first element in Old Norse rosmhvalr.