A sound imitating the lowing of oxen; also used to express contempt, disapprobation, aversion. Used subst. as a name for itself, esp. as the sound of hooting. Cf. BO, BOOHOO.
1801. R. Gill, in Chambers, Hum. Sc. Poems (1862), 176. He heard a boo ahint a hedge.
1855. Thackeray, Rose & Ring, viii. (1866), 48. He fell asleep and snored horridly. Booh, the nasty pig!
1884. Chr. World, 25 Sept., 717/1. The sibilant hiss and the contemptuous boo.
1885. Pall Mall Gaz., 6 Oct., 2/1. When the names of the agents came out, you should have heard the roar of savage boos.