[boo] interj [ME bo] (15c)--used to express contempt or disapproval or to startle or frighten
[2]boo n, pl boos (1575) 1: a shout of disapproval or contempt
2: any sound at all--usu. used in negative constructions "never said ~" [3]boo vi (1884): to deride esp. by uttering boo ~ vt: to express disapproval of by booing "the crowd ~ed the referee" [4]boo n [origin unknown] (ca. 1959): marijuana