Origins
"Autumn" is unusual among the English season names in being a borrowing rather than a native Germanic word. While "summer" and "winter" descend from Proto-Germanic roots of great antiquity, and "spring" was coined from native English material, "autumn" arrived in English from French, ultimately from Latin, probably displacing not one but two native competitors in the process.
The word entered Middle English in the 14th century as autumpne, borrowed from Old French autompne (modern French automne). The French form came directly from Latin autumnus (sometimes spelled auctumnus), the standard Roman term for the season between summer and winter, roughly September through November. The Latin word's ultimate origin is disputed. The most widely accepted hypothesis traces it to Etruscan, the pre-Roman language of central Italy, since several Roman religious and calendar terms (including many month names) were borrowed from Etruscan civilization. No convincing Indo-European etymology for autumnus has been established, which strengthens the case for a non-IE source.
Before "autumn" arrived, English had its own name for the season: "harvest," from Old English hærfest, which meant both the act of gathering crops and the season when this occurred. This is cognate with German Herbst (which still means "autumn"), Dutch herfst, and Old Norse haust. The Germanic root is *harbistaz, possibly related to PIE *kerp- ("to pluck, to gather"). For centuries, "harvest" served perfectly well as the English season name.
Latin Roots
The displacement of "harvest" by "autumn" occurred gradually during the 16th and 17th centuries, driven by the prestige of Latin and French learning in post-medieval England. As English absorbed massive amounts of Romance vocabulary during the Renaissance, the Latinate "autumn" gained ground in literary and educated usage. Meanwhile, "harvest" increasingly narrowed to mean only the act of gathering crops, losing its seasonal sense.
During the same transitional period, a third contender emerged: "fall," short for "fall of the leaf." This poetic phrase, describing the most visually dramatic feature of the season, appeared in English by the 1540s and was shortened to "fall" by the 1660s. For a time, English had three competing season names — harvest, autumn, and fall — all in active use.
The resolution differed on either side of the Atlantic. In British English, "autumn" won decisively, becoming the standard term by the 18th century. In American English, "fall" prevailed and remains the dominant term in everyday speech, though "autumn" is understood and sometimes used in more formal or literary contexts. This divergence is one of the classic examples of how British and American English evolved differently after the colonial period — American English preserved a form that was once common in Britain but fell out of favor there.
Later Development
The adjective "autumnal" (from Latin autumnālis) has been in English since the 15th century and remains the standard adjective for both "autumn" and "fall" — there is no widely used adjective "fally" or "fallish," giving "autumnal" unchallenged dominion in both dialects.
English stands alone among the Germanic languages in using a Latin-derived season name. German uses Herbst, Dutch uses herfst, Swedish uses höst, Danish uses efterår ("after-year"), Norwegian uses høst, and Icelandic uses haust — all native Germanic forms. This isolation reflects the uniquely heavy Romance influence on English vocabulary, a consequence of the Norman Conquest and the subsequent centuries of French cultural prestige in England.
The story of "autumn" is thus a microcosm of English linguistic history: a Latin word, filtered through French, arriving in a Germanic language and gradually displacing a native term through cultural prestige — while a parallel native coinage ("fall") survived in the branch of English that crossed the Atlantic.