A tusk is a front tooth or teeth that grows continuously, sometimes to several feet in length.
The word tusk is said to have come from the Old English words tux or tusc, which came from the Proto-Germanic tunthskaz word for "tooth".
The function of the tusk may be different in different species. Walruses use tusks in competition between males for females, in helping to haul out and move on ice and for boring breathing holes in the ice. The function of narwhal tusk is not known, but may have a sensory function.
Tusks, like other teeth, are composed of an inner pulp cavity surrounded by dentine (a calcareous material), which is covered by cementum (which attaches the tooth to the jaw bones). This is in turn covered with enamel, which may be found only on areas that are heavily used, such as the tip of the tusk.
Tusks are referred to sometimes as "ivory." Ivory can be used by humans to make carvings, jewelry, piano keys and inlays in furniture. Trade in ivory in many cases is restricted or illegal as it has contributed to the decline of species such as elephants.