We may now call it fall, but once upon a time, the season that comes after summer but before winter was referred to simply as harvest.
An old name for fall
According to the written record, harvest is the earliest name for the third season of the year. It’s found in Old English as hærfest, a word of Germanic stock, perhaps with underlying, ancient sense of “picking, plucking.”
The use of harvest specifically for the season fell out of use, becoming used more generally for when ripened crops are, well, harvested—gathered for processing and winter storage, roughly between August and November. Harvest can also refer to those ripened, gathered crops themselves.
Astronomically, the season lasts from the end of September until December (around the 21st of each month), between the autumnal equinox and the winter solstice in the Northern Hemisphere.
Why do we call it fall?
We have evidence for fall, as the name of the third season of the year, in the 1500s. It appears to come the notion of the falling of the leaves during this time of year, when deciduous trees shed their leaves.
Like harvest, fall is found in Old English, from Germanic roots, and its sense largely stayed the same. Now, fall was common in England until about the end of the 1600s, when it was ousted by autumn.
Recorded as early as the late 1300s, autumn is from the French autompne and Latin autumnus, whose deeper roots are obscure. Chaucer and Shakespeare both used it in their works, notably.
Now, American English speakers use both fall and autumn, though fall became more common in the US by the late 1800s. Speakers of British English largely use autumn.
Fall provides a nice foil to its opposite season, spring (from the idea of the spring of the leaf). It gives us the helpful reminder, “Spring ahead, fall back,” when we get confused about our clocks on daylight savings.