exclamation

said suddenly to surprise someone who is unaware of one’s presence.

‘Boo!’ she cried, jumping up to frighten him

noun

an utterance of ‘boo’ to show disapproval of a speaker or performer.

the audience greeted this comment with boos and hisses

verb

say ‘boo’ to show disapproval of a speaker or performer.

they booed and hissed when he stepped on stage