boo (interjection):
used to express contempt or disapproval or to startle or frighten
boo (noun):
a shout of disapproval or contempt
boo (noun):
any utterance at all; usually used in negative constructions
boo (verb):
to deride especially by uttering a prolonged boo
boo (verb):
to express disapproval of by booing (the crowd booed the referee)