crack up

Verb

crack up (third-person singular simple present cracks up, present participle cracking up, simple past and past participle cracked 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, usually passive, usually negative) To cry up; to extol.

   The job just can't be all that she 's cracked it up to be.

   It is not necessarily the great thing that the proponents are cracking it up to be.

   This new computer system is not what it was cracked up to be.

   It not nearly as good as it has been cracked up to be.

   I wonder whether it could be all it is being cracked up to be.

References

• crack up at OneLook Dictionary Search
• crack in The Century Dictionary, The Century Co., New York, 1911