crab 1 
(krăb)
(krăb)n.
1.
a. Any of various chiefly marine decapod crustaceans of the infraorder Brachyura, having a hard carapace that covers a broad flattened cephalothorax with a small abdomen tucked beneath it, and an anterior pair of legs that are large and pincerlike.
b. Any of various similar decapod crustaceans, such as a hermit crab or a king crab.
c. Crabmeat.
2.
a. A crab louse.
b. 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.
v. crabbed, crab·bing, crabs
v.intr.
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.
v.tr.
Idiom: 1. To direct (an aircraft) partly into a crosswind to eliminate drift.
2. To cause to move or scurry sideways.
catch a crab
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; see gerbh- in the Appendix of Indo-European roots.]
crabber n.