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1. verb To laugh a lot. We all cracked up at Josh's joke.
2. verb To cause someone to laugh a lot. In this usage, a noun or pronoun can be used between "crack" and "up." Josh's joke cracked us all up. That comedian just cracks me up.
3. verb To experience a mental or emotional breakdown. All those days of sleep deprivation finally caused me to crack up. She's terrified to leave the house all of a sudden—I think she's cracking up.
4. verb To destroy something. He drove into a tree and cracked up his car.
5. verb To be in an accident. I cracked up after losing control of my car.
6. noun An accident. When used as a noun, the phrase is typically hyphenated. I was in a crack-up when I lost control of my car and hydroplaned.
1. Past tense of crack up.
2. cracked up to be. Reputed to be. This expression is always used in a negative way, as in I don't think this book is all it's cracked up to be. It relies on the now obsolete use of to crack up to mean "to praise extravagantly." It appeared in The Kentuckian: "He is not the thing he is cracked up for" (May 28, 1829). [Early 1800s]
3. Under the influence of crack (a form of cocaine). For example, "Who's cracked up, who's cracked out, and who's dead?" ( World News Tonight, ABC-TV, May 12, 1992). [1980s]