crack up

Short definition from Wiktionary

Verb

1. 1
   To laugh: To laugh heartily.
2. 2
   To laugh: To cause to laugh heartily.
3. 3
   To laugh: To tease (someone) or tell jokes at the expense of (someone).
4. 4
   To break: To become insane; to suffer a mental breakdown.
5. 5
   To break: To break down or fall apart; to stop functioning; to shatter.
6. 6
   To break: To separate a group.
7. 7
   To break: To crash an aircraft or automobile.
8. 8
   To break: To remove the shell from nuts.
9. 9
   To break: To crack (petroleum). (to break down (a complex molecule), especially with the application of heat: to pyrolyse)
10. 10
    To affect the image of something: To praise or applaud (something); to promote a positive view of (something).
11. 11
    To affect the image of something: To insult, demean or harm the image of (something).
12. 12
    To affect the image of something: To cry up; to extol.
13. 13
    To smoke crack cocaine.

Adjective

1. 1
   Funny; hilarious

Noun

1. 1
   Alternative spelling of crackup.