crazy

The definition of crazy is someone or something that is insane or not mentally sound.

(adjective)

An example of crazy is an idea that makes absolutely no sense.
An example of crazy is a person who is in a mental hospital and who is yelling, hallucinating and otherwise acting like they are insane.

See crazy in Webster's New World College Dictionary

1. having flaws or cracks
2. shaky or rickety; unsound
1. unsound of mind; mentally unbalanced or deranged; psychopathic; insane
2. of or for an insane person
temporarily unbalanced, as with great excitement or rage
Informal foolish, wild, fantastic, etc.; not sensible: a crazy idea
Informal very enthusiastic or eager: crazy about the movies

Origin: < craze

interjection

Slang used to express approval, pleasure, wonder, etc.: now rare

noun pl. crazies

Slang an eccentric or mentally unbalanced person

Related Forms:

See crazy in American Heritage Dictionary 4

adjective cra·zi·er, cra·zi·est

Affected with madness; insane.
Informal Departing from proportion or moderation, especially:
a. Possessed by enthusiasm or excitement: The crowd at the game went crazy.
b. Immoderately fond; infatuated: was crazy about boys.
c. Intensely involved or preoccupied: is crazy about cars and racing.
d. Foolish or impractical; senseless: a crazy scheme for making quick money.