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.

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1801.  R. Gill, in Chambers, Hum. Sc. Poems (1862), 176. He heard a boo ahint a hedge.

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1855.  Thackeray, Rose & Ring, viii. (1866), 48. He … fell asleep and snored horridly. Booh, the nasty pig!

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1884.  Chr. World, 25 Sept., 717/1. The sibilant hiss and the contemptuous ‘boo.’

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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.’

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