Expressions of disapproval or contempt made by an audience, typically a prolonged 'boo' sound. Also the third-person singular present tense of the verb 'to boo', meaning to make such sounds.
Likely imitative of the sound itself, first recorded in English in the 18th century. The sound may derive from the Latin 'boare' (to cry aloud) or simply be a natural exclamation of disapproval found in many languages.
Booing is one of the few truly universal human expressions - nearly every culture has some version of this sound to express disapproval. Interestingly, audiences in ancient Roman theaters would 'hiss' rather than 'boo', and the modern 'boo' sound may have evolved from the practice of saying 'boo-hoo' to mock someone.
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