crab

1. 1. Any of various predominantly marine crustaceans of the division Brachyura within the order Decapoda, characterized by a broad flattened cephalothorax covered by a hard carapace with a small abdomen concealed beneath it, short antennae, and five pairs of legs, of which the anterior pair are large and pincerlike.
   2. Any of various similar related crustaceans, such as the hermit crab or king crab.
   3. A horseshoe crab.
2. 1. A crab louse.
   2. crabs Slang. Infestation by crab lice.
3. The maneuvering of an aircraft partially into a crosswind to compensate for drift.
4. A machine for handling or hoisting heavy weights.

1. To hunt or catch crabs.
2. To scurry sideways in the manner of a crab.
3. To drift diagonally or sideways, especially when under tow.
4. To direct an aircraft into a crosswind.

1. To direct (an aircraft) partly into a crosswind to eliminate drift.
2. To cause to move or scurry sideways.

catch a crab

1. To make a faulty stroke in rowing that causes the blade of the oar to strike the water on the recovery stroke.

[Middle English crabbe, from Old English crabba.]