crack up

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crack up

  1. (idiomatic, intransitive) To laugh heartily.
    It was hilarious. We were cracking up the whole time.
  2. (idiomatic, transitive) To cause to laugh heartily.
    The joke about the nuns in the bath cracked me up.
  3. (intransitive, idiomatic) To become insane; to suffer a mental breakdown.
    She got through the war, but cracked up when her sister died.
  4. (transitive, informal, now usually passive) To cry up; to extol.
    This new computer system is not what it was cracked up to be.