Is it farther or further?
1650s, from Danish and Norwegian narhval, probably a metathesis of Old Norse nahvalr, literally "corpse-whale," from na "corpse" + hvalr "whale" (see whale). So called from resemblance of its whitish color to that of dead bodies. The first element is from PIE *nau- "death; to be exhausted" (cf. Old English ne, neo, Gothic naus "corpse," Old Cornish naun, Old Church Slavonic navi, Old Prussian nowis "corpse," Lettish nawe "death," Lithuanian novyti "to torture, kill").