- boo
- "to startle," early 15c., boh, "A combination of consonant and vowel especially fitted to produce a loud and startling sound" [OED, which compares L. boare, Gk. boaein "to cry aloud, roar, shout."]; as an expression of disapproval, 1801 (n.), 1816 (v.); hence, the verb meaning "shower someone with boos" (1893). To say boo "open one's mouth, speak," originally was to say boo to a goose.