narwhal (n.)

"sea-unicorn, dolphin-like Arctic sea mammal" (one of the teeth of the male is enormously developed into a straight spirally fluted tusk), 1650s, from Danish and Norwegian narhval, probably a metathesis of Old Norse nahvalr, literally "corpse-whale," from na "corpse" (see need (n.)) + hvalr "whale" (see whale). If this is right, it likely was so called from its whitish color, resembling that of dead bodies. But according to nature writer Barry Lopez ("Arctic Dreams"), Winfred P. Lehmann, professor of Germanic linguistics, suggested the name was folk-etymology and said nahvalr was a West Norse term meaning "whale distinguished by a long, narrow projection."