boo(1) (iou)

boo interjection, noun2, & verb. [bu:] E19.
[Imit.: cf. BO interjection & noun2.]
A. interjection & noun. A prolonged sound expressing derision or disapproval, or an exclamation intended to startle. Occas., a sound (as) of cattle lowing. E19.
can't say boo to a goose is very timid or shy.
b. verb trans. & intrans. Make such a sound (at); jeer (a person, an action, etc.). E19.
booer noun E20.