Fanny is a diminutive of Frances. Frances originates in Latin language and means "woman from France". It is a feminine form of Francis. Frances was the name of the 19th century saint as well as the name of a famous 1982 film, starring Jessica Lange. As a feminine given name it has been fairly popular in the United States. At the beginning of the 20th century, Fanny started being used as vulgar slang word in English and the name has not been used since. That does not apply to other languages than English, where Fanny is still fairly common.