vagina n.

"sexual passage of the female from the vulva to the uterus," 1680s, medical Latin, from specialized use of Latin vagina "sheath, scabbard, covering; sheath of an ear of grain, hull, husk" (plural vaginae), a word of uncertain origin. Perhaps cognate with Lithuanian vožiu, vožti  "to cover with a hollow thing," but de Vaan points out that "Obviously, this is a gratuitous proposal." A modern medical word; the Latin word was not used in an anatomical sense in classical times. Anthropological vagina dentata is attested from 1902.