1655, from Du. walrus, which was probably a folk-etymology alteration (by influence of Du. walvis "whale" and ros "horse") of a Scand. word, such as O.N. rosmhvalr "walrus," hrosshvalr "a kind of whale," or rostungr "walrus." O.E. had horschwæl, and later morse, from Lapp morsa or Finnish mursu, which may ult. be the source, much garbled, of the first element in O.N. rosmhvalr.