Real Dictionary

crack in American English
intransitive verb: to break without complete separation of parts; become fissured
transitive verb: to cause to make a sudden sharp sound

crack in American English 1
to make a sudden, sharp noise, as of something breaking

crack in American English 2
designating or of cocaine in this form
hard, pebblelike pieces of highly purified cocaine prepared for smoking: a highly potent and addictive form of cocaine

crack in British English
verb: to break or cause to break without complete separation of the parts

crack in Mechanical Engineering
noun: A crack is a long thin hole with sharp ends in a material.

crack noun and adjective uses
countable noun: A crack is a very narrow gap between two things, or between two parts of a thing.
singular noun: If you open something such as a door, window, or curtain a crack, you open it only a small amount.

crack verb uses
verb: If something cracks, or if you crack it, it makes a sharp sound like the sound of a piece of wood breaking.
verb: If something hard cracks, or if you crack it, it becomes slightly damaged, with lines appearing on its surface.
verb: If you crack a hard part of your body, such as your knee or your head, you hurt it by accidentally hitting it hard against something.