In American English, fanny is a relatively innocent word for “buttocks”, but in British English, it can serve as a much more offensive slang term for “vagina” (or, metonymically, women in general). It’s gotten to the point where some movies and television shows from the US have to be censored on the other side of the Atlantic. The American meaning evolved from the British one in the 1920s for unclear reasons associating the two body parts, and the British meaning probably comes from the name of the protagonist of a controversial mid-eighteenth century novel, Fanny Hill, where the main character Frances (nicknamed with the diminutive Fanny) has numerous sexual encounters and thus got associated with the vagina. Finally, the name Frances traces to the Latin demonym Francisus, meaning “Frankish”.
