Narwhal (Monodon), a genus of toothed whales, of the Dolphin family, with one species (M. monoceros), from the Arctic seas of both hemispheres. The adult male possesses a long, spirally - twisted tusk or "horn," really the abnormally developed canine tooth of the left side; the tooth on the right is very rarely developed, though this sometimes occurs. It is rarely present in females, though Scoresby found a female with a tusk over four feet long. The use of these weapons is unknown. The body of a full-grown male may be 14 feet long, and the tusk from 6 feet to 10 feet. The general colour of the youug is bluish-grey; older animals are lighter with dark spots. Narwhals are hunted for the oil they yield, and the ivory of their tusks.