There are 2 definitions of crack up in English:

crack up1

informal
1Suffer an emotional breakdown under pressure.
More example sentences
  • I was short-tempered and I was cracking up a bit under the pressure of it all.
  • ‘If I had not had Diana and the children I would have cracked up and had a mental breakdown by now,’ he said.
  • His stylish arthouse flick looks at three women as they crack up.
2 (also crack someone up) Burst or cause to burst into laughter.
More example sentences
  • He cracks up into laughter, his shoulders heaving uncontrollably.
  • I really cracked up in laughter when I read the headline ‘Protest is the backbone of democracy’.
  • Before I knew it I was buzzed and cracking up with laughter.
See parent entry: crack

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There are 2 definitions of crack up in English:

crack-up2

Syllabification: crack-up
Pronunciation: /ˈkrakəp
 
/
(also crackup)

noun

[usually in singular] informal
1A collapse under strain: he had a complete mental crack-up
More example sentences
  • Mark has had one emotional crack-up and one hospitalisation before the stresses have even begun.
  • The directorial debut shows the actress grappling with the aftermath of a crack-up.
  • By the time the reader gets to book four, Donny's been ‘hospitalized for a crack-up.’
2An act of breaking up or splitting apart: the crack-up of a political system
More example sentences
  • It would lead to the crack-up boom and the breakdown of the whole monetary system.
  • Any bump in the road is greeted not just as evidence of the crack-up, but as its beginning.
  • The later the crack-up comes, the longer the period in which the calculation is misguided by fiduciary media.
3A car crash: motorists were asked to report minor crack-ups later

Definition of crack up in: