Other forms: craziest, crazier
Crazy is the everyday word for something with no sense in it at all. A plan to drive nine hours for a two-hour party, a price that makes you laugh out loud, an afternoon that goes from hail to sunshine and back.
It also means wildly keen: crazy about someone, football-crazy, going crazy for a new album. Piled in front of another word it just means very — crazy expensive, crazy good. Two warnings. It is informal, so keep it out of reports and letters. And aimed at a person with a mental illness it works as an insult, so English is moving away from it there: the plan can be crazy, the patient should not be. Drive someone crazy is the common phrase, and like crazy means at full tilt.
1adjectivecrazyCompletely lacking sense; wild or reckless.
“It was a crazy idea and it worked.”
2adjectiveenthusiasticExtremely enthusiastic about someone or something.
“He has been crazy about trains since he was four.”
3adjectivegreatExtreme; very great.
“The queue outside the shop was crazy.”
Too few real examples of this word to estimate which sense is commonest.
Also accepted in games: mad, insane
Crazy is craze plus -y, and craze once meant to crush or crack. A crazy person was a cracked one, which is why English still says crack up for a breakdown and crackpot for someone whose thinking has broken. Old pottery with fine cracks through the glaze is called crazed for the same reason.
From craze + -y, akin to being "crazed up". Compare crack up (“suffered a mental breakdown; be insane”), crackpot. Compare typologically чо́кнутый.
Etymology from Wiktionary, CC BY-SA