A sudden emotional outburst or loss of control; also, a wild party or extreme experience, especially in 1960s counterculture.
From 'freak' plus 'out' (Old English 'ūt'), forming a phrasal verb 'freak out' that became a noun through a process called nominalization. Emerged as slang in 1960s hippie culture.
'Freak out' started as a verb phrase ('to freak out') in the 1960s counterculture and was then nouned into 'freakout'—a perfect example of how modern English recycles its own words into new forms at incredible speed.
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