Narwhal, a cetacean mammal, of the genus monodon (Linn.), frequenting the arctic seas; it- popular name is sea unicorn. It has no proper teeth, but in the males, and sometimes in the females, there are two tusks arising from the intermaxillary bone; these are true incisors, but only one, usually the left, is developed, the other remaining rudimentary in most cases; the former is long, pointed, spirally twisted ami grooved, and directed straight forward, growing through life from a permanent pulp as in the elephant. The tusk, of solid ivory and 6 or 8 ft. long, is a most formidable weapon when wielded by such an active and powerful animal, and is sometimes driven deeply into the timbers of a ship. According to Mulder there are two small teeth in the gum of the upper jaw. In the only well ascertained species (M. monoreros, Linn.) the body may attain a length of 15 or 16 ft. and the tusk from to 10 additional; there is no well marked sepration between the head and body; the forehead rises suddenly, and the blow-hole is on the top of the head; the eyes and mouth are small, and the lips unyielding; the pectorals are small for the size of the animal; the caudal is transverse, bilobed, and about 4 ft, wide; instead of a dorsal fin there is a low fatty ridge 2 or 3 ft. long in the middle of the back.
The prevailing color is dark gray above with numerous darker spots, white on the sides and below, on the former with grayish spots; some specimens are very light-colored, and the young are said to be bluish gray. The food consists principally of cephalopod mollusks, and, on the authority of Scoresby, of flat and other fishes, which it transfixes with its horn; other uses of this weapon are for breaking the ice for the purpose of obtaining air, and for defence. Narwhals are sometimes seen in bands of 10 to 20, sporting about whaling ships, elevating their tusks above the water, and playing about the bows and rudder; they are migratory, and their appearance is hailed with delight by the Greenlanders, who consider them the certain forerunners of the right whale; and this, the result of their experience, is probably due to both using the same kind of food. They are harpooned for their ivory, oil, and flesh; the last is considered a delicacy as food by the Greenlanders. The blubber is from 2 to 4 in. thick, and yields a very superior oil.
The ivory of the tusk is very hard and white, and takes a high polish; it was formerly a valuable article of commerce, when the origin of the horns was less known; a famous throne of the kings of Denmark is said to be made of the ivory of narwhals' tusks.