Nar"whal (?), n. [Sw. or Dan. narvhal; akin to Icel. nāhvalr, and E. whale. the first syllable is perh. from Icel. nār corpse, dead body, in allusion to the whitish color its skin. See Whale.] [Written also narwhale.] (Zoöl.) An arctic cetacean (Monodon monocerous), about twenty feet long. The male usually has one long, twisted, pointed canine tooth, or tusk projecting forward from the upper jaw like a horn, whence it is called also sea unicorn, unicorn fish, and unicorn whale. Sometimes two horns are developed, side by side.

• an Arctic cetacean, about 20 feet long; the male has a single twisted pointed canine tooth or tusk projecting forward like a horn.