Meaning

noun a young waitress in a nightclub whose costume includes the tail and ears of a rabbit

noun (usually informal) especially a young rabbit

originFrom bun (“rabbit”) + -y (diminutive suffix). Probably from Scottish Gaelic bun (“bottom, butt, stump, stub”), from Old Irish bun (“the thick end of anything, base, butt, foot”), from Proto-Celtic *bonus, though its origin is uncertain. Compare also English bum. Together with rabbit, bunny has largely displaced its former rhyme cony (see cony for more).

Etymology from Wiktionary, CC BY-SA 3.0