An eccentric or crazy person; someone with strange or unconventional ideas or behavior.
American slang of uncertain origin, possibly from 'cuckoo' (the bird associated with madness) or from Australian slang. First appeared in printed English in the 1960s, especially in surfing culture.
In the 1960s, 'kook' was primarily a surfing insult for a beginner, but it eventually lost its mean edge and now just means an interesting weirdo! The same word can shift from nasty to friendly over time.
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