Of Latin and/or Greek origin.
Fanny is diminutive for the names Frances, Françoise, and Stephanie.
From the Latin name Franciscus, meaning “Frenchman”.
Also by association with the name Frank, it means “frank”.
Fanny may also be a diminutive of Stephanie.
When so, it derives from the Greek name “Στέφανος”, (Stefanos), and the Greek word “στέφανος”, meaning “wreath”.
In the English speaking countries, the name is kind of a taboo, because, since the end of the 19th c. it’s been used as a slang for “buttock”.
The French name Fanny though, it pronounced Fanný.
The name was ranked #231 in France (2016).
Other forms of the name are Fannie, Fanni, Fania.
Famous bearers are Fanny Ardant, Fanny Rinne, Fanny Rask, Fanny Mendelssohn, Fanny Crosby.