A crustaceous fish of the genus Cancer. Lobsters have large claws and fangs, and four pair of legs. They are said to change their crust annually, and to be frightened at thunder or other loud report. They constitute an article of food.

Any large macrurous crustacean used as food, esp. those of the genus Homarus; as the American lobster (H. Americanus), and the European lobster (H. vulgaris). The Norwegian lobster (Nephrops Norvegicus) is similar in form. All these have a pair of large unequal claws. The spiny lobsters of more southern waters, belonging to Palinurus, Panulirus, and allied genera, have no large claws. The fresh-water crayfishes are sometimes called lobsters.