Why is “autumntime” (or “falltime”) not a word?
- wintertime => sure
- springtime => fine
- summertime => lovely
But apparently autumn/fall has no equivalent. Why?
The Anglo-Saxon calendar only had two seasons, winter and summer, each six months long. They had words for other periods of the year, but they weren’t considered seasons.
At some point near the beginning of Middle English1, a four-season calendar was adopted. However, the other two seasons didn’t have definite names. We can see from the OED that their names fluctuated for a while before settling into spring and fall or autumn.
c1050: Þa feower timan..lengten, sumor, hærfest, & winter.
a1387: Þe evenes of þe day and þe nyȝt is ones in þe Lente and efte in hervest.
1545: Spring tyme, Somer, faule of the leafe, and winter.
It seems from these quotes that we might easily have had lent (a shortened form of lengthen) and harvest as names for spring and autumn, as these were common names for these seasons in Middle English.
It also appears that the "long forms" of the names for the seasons were "spring time", "harvest time", and "fall of the leaf". This explains why we don’t say "fall time".
The word "autumn" was borrowed from Old French in the 16th century, well after "springtime", "summertime", "harvesttime", and "wintertime" were established, and for some reason these phrases were not extended to "autumntime", even though it would have been a very logical development in English. Maybe people used "spring time" and "harvest time" more often earlier because "spring" and "harvest" weren’t yet established words for seasons (as "summer" and "winter" were).
1 This probably didn’t happen at a single point in time. The quote from the OED ca. 1050 lists four seasons. However, the song "Sumer Is Icumen In", which Wikipedia says was composed in the 13th century, is clearly about spring.