in ichthyology, a genus of fishes belonging to the order of cetaceans. It has a long wreathed tooth in the upper jaw, which perforates the upper lip, and has the appearance of a horn; from this circumstance it has got the name of the unicorn-fish. It is the narwhal of Pontopiddan, and is of the whale kind. Sometimes it grows to 25 feet in length; but the usual size is from 16 to 20.