or Crab, in zoology, a genus of insects belonging to the order of insecta aptera. The generic characters are these: They have eight legs, (feldom ten or fix), besides the two large claws which answer the purpose of hands. They have two eyes at a considerable distance from each other, and for the most part supported by a kind of pedunculi or foot-stalks; the eyes are likewise elongated and moveable. They have two clawed palpi; and the tail is jointed. There are no less than 87 species of cancer, distinguished principally by the length of their tails and the margins of their breasts. This genus includes the lobster, shrimp, &c.

in medicine, a roundish, unequal, hard, and livid tumour, generally seated in the glandulous parts of the body, supposed to be so called, because it appears at length, with turgid veins shooting out from it, so as to resemble, as it is thought, the figure of a crab-fish; or, as others say, because, like that fish, where it has once got, it is scarce possible to drive it away. See Medicine, and Surgery.

in astronomy, one of the twelve signs of the zodiac, represented on the globe in the form of a crab; and thus marked (♋) in books.

Tropic of Cancer, in astronomy, a lesser circle of the sphere parallel to the equator, and passing through the beginning of the sign cancer.