n.
      - a narrow opening between two parts of something which has split or been broken.
- a sudden sharp or explosive noise. ▸a sharp blow. 
- informal a joke or jibe.
- 
(also craic)
 chiefly Irish enjoyable entertainment; a good time. ▸Scottish & N. English a conversation. 
- informal an attempt to do something.
- 
(also crack cocaine)
 a potent hard crystalline form of cocaine broken into small pieces.
v.
         - break or cause to break with little or no separation of the parts.
- give way under pressure or strain. ▸
(crack up)
 informal suffer an emotional breakdown under pressure. ▸
(crack up)
 informal burst into laughter. 
- make or cause to make a sudden sharp or explosive sound. ▸hit hard. 
- (of a person's voice) suddenly change in pitch, especially through strain.
- 
(crack down on)
 informal take severe measures against.
- informal solve, interpret, or decipher. ▸break into (a safe). 
- 
(crack on)
 Brit. informal proceed or progress quickly.
- tell (a joke).
- decompose (hydrocarbons) by heat and pressure to produce lighter hydrocarbons.
adj.
 very good or skilful:
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 a crack shot.
Phrase
  
  Derivative
  
  Etymology
  OE cracian ‘make an explosive noise’; of Gmc origin.