We think of “fall” as being a peculiarly American description of this season, but it appears that this was the typical Old English name. The word probably comes from the Old English “feallan”, meaning to decay or die. In particular, the season was called “fall” to represent the fall of the leaf – as can be seen from this picture. “Fall” and “autumn” are believed to have been equally popular ways to describe this season up until around the 1600s and early 1700s.
Over time, “fall” fell (sorry) out of use in British English, but continued to be popular in the USA. And that is why we now have two very different words for the same season.