Definition of crack up phrasal verb from the Oxford Advanced Learner's Dictionary

 

crack up

 phrasal verb
phrasal verb
 
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Phrasal Verbs
  1. 1to become ill, either physically or mentally, because of pressure You'll crack up if you carry on working like this.
  2. 2to start laughing a lot He walked in and everyone just cracked up.
(informal) to make somebody laugh a lot Gill's so funny, she just cracks me up.
See the Oxford Advanced American Dictionary entry: crack up