n 1  :  any of a tribe (Brachyura) of chiefly marine crustaceans with a short broad usu. flattened carapace, a small abdomen that curls forward beneath the body, short antennae, and the anterior pair of limbs modified as grasping pincers  2  crabs  pl  :  infestation with crab lice .
 
 
 
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