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Definition of CRAB
pluralcrabsalsocrab: any of numerous chiefly marine broadly built decapod crustaceans:
a: any of an infraorder (Brachyura) with a short broad usually flattened carapace, a small abdomen that curls forward beneath the body, short antennae, and the anterior pair of limbs modified as grasping pincers
b: any of various crustaceans of an infraorder (Anomura) resembling true crabs in the more or less reduced condition of the abdomen
Middle English crabben, probably back-formation from crabbed
First Known Use: 1662
Medical Definition of CRAB
: any of a tribe (Brachyura) of chiefly marine crustaceans with a short broad usually flattened carapace, a small abdomen that curls forward beneath the body, short antennae, and the anterior pair of limbs modified as grasping pincers
crabspl: infestation with crab lice
Common swimming crab (Portunus holsatus), showing its paddle-shaped feet—Dr. Eckart Pott/Bruce Coleman Ltd.
Any of 4,500 species of short-tailed decapod, found in all oceans, in freshwater, and on land. Its carapace (upper body shield) is usually broad, and its first pair of legs is modified into pincers. Most crabs live in the sea and breathe through gills, which in land crabs are modified to serve as lungs. They walk or crawl, generally with a sideways gait; some are good swimmers. Crabs are omnivorous scavengers, but many are predatory and some are herbivorous. Two of the largest known crustaceans are the giant crab of Japan (13 ft, or 4 m, from claw tip to claw tip), a spider crab; and the Tasmanian crab (up to 18 in., or 46 cm, long, and weighing more than 20 lbs, or 9 kg). Other species are less than an inch long. Well-known crabs include the hermit crab, edible crab (Britain and Europe), blue crab, Dungeness crab, fiddler crab, and king crab.