noun.any of numerous chiefly marine broadly built decapod crustaceans:

noun.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

noun.any of various crustaceans of an infraorder (Anomura) resembling true crabs in the more or less reduced condition of the abdomen

verb.to fish for crabs

verb.to move sideways indirectly or diagonally

verb.to crab an airplane

noun.crab apple

noun.an ill-tempered person: grouch

verb.to make sullen: sour

• old age has crabbed his nature
• always crabs about the weather

verb.to complain about peevishly

verb.spoil, ruin