Merriam-Webster Online Dictionary
boo (interjection) - used to express contempt or disapproval or to startle or frighten
1.
a shout of disapproval or contempt
2.
any utterance at all - usually used in negative constructions never said boo
intransitive verb
transitive verb
to deride especially by uttering a prolonged - boo to express disapproval of by booing - the crowd booed the referee
Merriam-Webster Online Thesaurus
boo (noun)a vocal sound made to express scorn or disapproval
SYNONYMS:
bird, boo, Bronx cheer, hiss, hoot, jeer, raspberry, razz, snortRELATED WORDS:
smirk, sneer, snicker, snigger; gibe ( jibe), put-down, taunt; whistleNEAR ANTONYMS:
applause, clapping