The stretch after midday
Afternoon, in ordinary English, is the part of the day that begins at noon and runs toward evening. Speakers treat the edges loosely: lunchtime, sunset, supper, or about six o’clock can all serve as the far end. The same noun can name a later chapter of a life or an era, the fading half of a prime. Informally it can even mean a gathering held in those hours. The shape of the word matches the meaning with unusual honesty.
The origin of the word afternoon is a native English compound, not a loan from French or Latin as a whole. Middle English already had afternone and after-non by the thirteenth century. Merriam-Webster dates the first known use to that century; other historical dictionaries place the noun around 1300. Either way, the form is a frozen phrase: after noon, the time once noon has gone by. The Middle English Dictionary reads the noun as the span between the noon meal and the evening meal. That gloss is worth holding onto. Medieval days were cut by eating and by church hours as much as by numbered clocks.
Two older pieces, joined in English
After is inherited. Old English æfter worked as an adverb and a preposition: behind in space, later in time, and sometimes in pursuit. Its inner build is a comparative. The base is of, in the sense off or away, plus a suffix -ter, so the oldest idea is farther off. Germanic relatives sit close by: Old Norse eptir, Old Frisian efter, Dutch achter, Old High German aftar, Gothic aftra. Farther out, Greek apotero (farther off) and Old Persian apataram (further) show the same comparative pattern. Nothing in that history is obscure, and nothing in it needs a folk story.
Noon is the half that hides a change of clock. Old English non did not first mean twelve. It named the ninth hour of daylight, about three in the modern afternoon by Roman and ecclesiastical counting, and it also named the canonical hour of nones. The source is Latin nona hora, the ninth hour, from nona, the feminine of nonus (ninth), from novem (nine). From the twelfth century the English sense began to slide toward midday. By the fourteenth century the move from the ninth hour to the sixth was largely finished. Dutch noen made a similar shift. Historians do not agree on a single cause. Medieval timekeeping was rough. Hours of daylight stretched and shrank with the seasons in northern latitudes. In monasteries, fasting often ended at nones, which may have pulled the named hour earlier. The secular midday meal may have moved forward as well. Any of those pressures, or several at once, could have helped. The important point for the compound is simpler: by the time afternoon is attested, noon was already becoming the hinge of the day rather than a mid-afternoon church mark.
So the word is English in its making. One of its parts, however, is a Latin hour-name that had already changed jobs inside English. That is inheritance plus an internal shift, not the borrowing of a ready-made foreign compound.
How the noun sat in a sentence
In the fifteenth and sixteenth centuries English often said at afternoon, as if the noun were a named office of the day rather than a container of hours. Around 1600 the now-usual in the afternoon takes over. The adjective, of the kind that modifies a walk or a light, is recorded from the 1570s. Middle English also had aftermete from the mid-fourteenth century: the stretch after the noon meal. That rival faded. Forenoon, the matching stretch before midday, survived as the transparent counterpart.
A figurative sense is already old. Late-sixteenth-century English could speak of the afternoon of a person’s best days, meaning the later, waning half of a prime. Modern dictionaries still list that use. The social sense, an afternoon as a party, is informal and later.
Because the build is so clear, other Germanic languages invented similar names instead of taking the English word. German Nachmittag and Dutch namiddag both mean after-midday. They are parallel compounds, not descendants of afternoon. English afternoon did travel, though, into Pacific creoles: Bislama aftenun, Pijin aftanun, and Tok Pisin apinun.
What the older noon still implies
The kink in the history is not after. It is that noon once pointed later than it does now. If Old English non still meant about three, then a phrase after non would have named a thinner, later slice of daylight than modern afternoon does. By the thirteenth and fourteenth centuries that older clock had largely given way, so the new compound named the long post-midday stretch speakers still mean. From the seventeenth to the nineteenth century, noon could even mean midnight in the phrase the noon of the night: a high point of a cycle, not only a mark on a daytime dial.
The Middle English reading between two meals is the detail that stays sharp. Afternoon did not begin as an abstract twelve-to-six block. It began as the hours after a named meal, in a day divided by food, prayer, and light. The clocks caught up. The compound stayed.