No PIE in Autumn
Fall is about leaves.
After the summer, the harvest. In fact, harvest was the name for this season until autumn came along. The word comes from the Latin autumnus, but we're not sure of its origin before that. Autumn is one of those words for which we can't definitively reconstruct a PIEroot. It could be from PIE roots *h₃ewǵ- (cold) or *h₂sows- (dry), but the ancient Etruscan autu- is a more attractive possibility.
You read that right: there's no PIE in autumn, which is the preferred term in the UK.
That's why Americans call the season fall instead. Thanksgiving would be dismal without pie, and fall comes from the PIE root *pol- (to fall). Just as leaves burst forth in spring, in fall they fall—the name of season is short for fall of the leaf.
Happy autumn, and I hope you get some pie!
Proto-Indo-European. See Greetings from Proto-Indo-Europe.
In parts of the northeast of England, some people call late autumn back end.