boo 1 
(b)
(b)n. pl. boos
1. A sound uttered to show contempt, scorn, or disapproval.
2. Informal Any sound or word: You never said boo to me about overtime.
interj.
Used to express contempt, scorn, or disapproval or to frighten or surprise another.
v. booed, boo·ing, boos
v.intr.
To utter a boo.
v.tr.
To express contempt, scorn, or disapproval of by booing: booed the singer off the stage.
[Imitative.]