any chiefly marine decapod crustacean of the genus Cancer and related genera (section Brachyura), having a broad flattened carapace covering the cephalothorax, beneath which is folded the abdomen. The first pair of limbs are modified as pincers See also fiddler crab, soft-shell crab, pea crab, oyster crabrelated adjective cancroid
any of various similar or related arthropods, such as the hermit crab and horseshoe crab
O.E. crabba, from a general Gmc. root (cf. Low Ger. krabben "to scratch, claw"). The constellation name is attested in Eng. from c.1000; the Crab Nebula (1868), however, is in Taurus, and is so called for its shape. Crab "fruit of the wild apple tree" (early 15c.) may be from unrelated Scandinavian scrab, of obscure origin. The combination of "bad-tempered, combative" and "sour" in the two words naturally yielded a meaning of "complain irritably," which is pre-1400. Crabgrass is c.1600, originally a marine grass of salt marshes; modern meaning is from 1743.