crack-up (n.)

1926, in reference to airplane crashes; 1936, "disintegration under stress, mental collapse" [Fitzgerald]; from the verbal phrase, from crack (v.) + up (adv.). The verbal phrase in the meaning "to break up laughing" is by 1967, transitive and intransitive. Its earliest sense was "to praise extravagantly" (as in not all it's cracked up to be).