September 22 marked the autumnal equinox and the first day of fall, which got us wondering: Why do we call the seasons Spring, Summer, Fall, and Winter?
Before Spring was called Spring, it was called Lent in Old English. Starting in the 14th century, that time of year was called “springing time”—a reference to plants “springing” from the ground. In the 15th century this got shortened to “spring-time,” and then further shortened in the 16th century to just “spring.”
“Summer” came from the Old English name for that time of year, sumor. This, in turn, came from the Proto-Germanic sumur-, which itself came from the Proto-Indo-European root sam- (sam- seems to be a variant of the Proto-Indo-European sem-, meaning “together / one").
The origin of “fall” as a name for a season isn't perfectly clear, though it’s thought that it probably came from the idea of leaves falling from trees (particularly the contraction of the English saying “fall of the leaf"). It first popped up as a name for a season in late-16th century England and became particularly popular during the 17th century, at which point it made its way over to North America. “Autumn,” meanwhile, came to English via the Old French autompne, from the Latin autumnus. From here, things get murky, but it’s thought autumnus probably came from an Etruscan word and is possibly related to the Latin augere, meaning “to increase.”
Calling the season autumn first occurred in English in the 12th century, though was a rarity until around the 14th century. It then began to pick up steam and became common in the 16th century—about the same time “fall” popped up as the name for the season. Before the season was autumn or fall in English, though, it was called “harvest.”
“Winter,” meanwhile, derives from the Proto-Germanic wentruz. This, in turn, probably comes from the Proto-Indo-European (PIE) wed, meaning “wet,” or it may come from the PIE wind-, meaning “white.” Either way, the Proto-Germanic wentruz gave rise to the Old English “winter” as the fourth season of the year, and the name for the season has stuck around ever since.
Incidentally, you may also wonder why the seasons are called seasons. The word “season” in this context comes from the Old French seison, meaning “sowing / planting.” This in turn came from the Latin sationem, meaning “sowing.” Initially, this referred to actually sowing seeds, but later, as with the Old French seison, it shifted definition to refer to the time period when you sow seeds, so literally “seed-time." Season in this sense in English popped up around the 13th century. It was also around this time that season was first used to refer to seasoning food—in this case from the Old French assaisoner, meaning “to ripen.”
Additional Source: Barnhart Concise Dictionary of Etymology