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English definition of “boo”

boo

exclamation     /buː/
an expression, usually shouted, used to surprise and frighten someone who does not know you are near them: She jumped out of the cupboard and shouted 'Boo!'.InterjectionsSounds used as interjections
(Definition of boo exclamation from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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