(informal) To open up one's books, especially in order to study.

present participle of crack a book

(slang) An intergluteal cleft visible due to low-riding pants, especially when one is bending over.

(slang) Very addicting.

(slang, UK, Australia, transitive) To flirt with; to approach and speak to (someone), seeking romance, love, sex, etc.

plural of crack-pipe

An outdoor children's game in which participants try to maintain hold of hands as random movements by the leader at the head of the line increase the force at the tail, as with the end of a whip.

(figuratively) To make harsh demands in a position of leadership.

Alternative form of crack-the-whip

wisecracking; making jokes or witty comments