Source : Webster's Revised Unabridged Dictionary (1913)

Narwhal \Nar"whal\, n. [Sw. or Dan. narvhal; akin to Icel.
   n[=a]hvalr, and E. whale. the first syllable is perh. from
   Icel. n[=a]r corpse, dead body, in allusion to the whitish
   color its skin. See {Whale}.] [Written also {narwhale}.]
   (Zo["o]l.)
   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.

Source : WordNet®

narwhale
     n : small arctic whale the male having a long spiral ivory tusk
         [syn: {narwhal}, {narwal}, {Monodon monoceros}]