1. [n]  the act of cracking something
2. [n]  a sudden sharp noise; "the crack of a whip"; "he heard the cracking of the ice"
3. [n]  the process whereby heavy molecules of naphtha or petroleum are broken down into hydrocarbons of lower molecular weight (especially in the oil-refining process)
4. [adj]  (informal) very good; "a bully pulpit"; "a neat sports car"; "had a great time at the party"; "you look simply smashing"
5. [adj]  making a loud sharp sound as of a rifle shot or a breaking branch or a whip; "lion tamers with their cracking whips"

cracker