1. The crab or crab-fish. This genus of animals have generally eight legs, and two claws which serve as hands; two distant eyes, supported by a kind of peduncles, and they are elongated and movable. They have also two clawed palpi, and the tail is jointed. To this genus belong the lobster, shrimp, cray-fish, etc.
2. In astronomy, one of the twelve signs of the zodiac, represented by the form of a crab, and limiting the suns course northward in summer; hence, the sign of the summer solstice.
3. In medicine, a roundish, hard, unequal, scirrous tumor of the glands, which usually ulcerates, is very painful, and generally fatal.