One spelling, two words
In present-day English, fair does more work than a short word should. A decision can be fair. A sky can be fair. Hair can be fair. A result can be only fair. A town can hold a fair. Those uses share letters and a sound, but they do not share a single history. English keeps two different words under this spelling: a native Germanic adjective (and the adverb built from it), and a later Romance noun for a market, feast, or exhibition.
The loudest cluster now is the one around justice and adequacy: fair treatment, a fair share, playing fair. Beside them sit older literary and weather senses still alive in set phrases: a fair maiden, fair weather, a fair wind. The gathering noun is a homonym. A village fair may be a pleasant day, but that overlap is accident, not descent.
Inherited from Old English
The adjective is home-grown. Old English had fæger, already covering several kinds of pleasantness: a person, body, object, or place pleasing to look at; weather that was bright, clear, and not rainy; and, by late Old English, moral goodness. The related adverb fægere meant beautifully. Middle English carried the word forward in many spellings, among them fayr, fager, and fair, with comparatives such as fairer and superlatives such as fairest, before the modern form settled.
Standard historical dictionaries place this adjective in English before the twelfth century, which is another way of saying it was already ordinary in the Old English period. It is inherited from Germanic, not taken from French or Latin. Cognates include Old Saxon fagar, Old High German fagar, Old Norse fagr, and Gothic fagrs. In the North Germanic languages the descendant is still a living word for beauty: Icelandic fagur, and Swedish, Danish, and Norwegian fager, all in the region of pretty or beautiful. Gothic is the most revealing cousin, because fagrs there means fit or suitable, closer to an older layer than to later English handsome.
There is no prefix or suffix to unpack: a simple stem plus ordinary comparative and superlative endings. Homophones can mislead. Fare as a ticket price or a journey comes from a different Old English family, the one behind faran, to go. Fairy is another word again.
The deeper root is not settled
Beyond Proto-Germanic fagraz (and the West Germanic fagr that feeds Old English), reconstructions disagree. One proposal ties the form to a Proto-Indo-European root glossed roughly as to make pretty, and compares Lithuanian puošiu, I decorate. Another, now common in reference works, starts from peh₂ḱ-, a root of attaching, joining, and coming to terms. On that view the Germanic adjective sits near Latin pax, peace, and pangere, to fix or fasten, and near Greek verbs for making something firm. The Oxford English Dictionary also notes that a second Indo-European base, the one behind English fain, would have merged with this one in Germanic sound change, so the family tree is not a single clean line.
None of those deeper links is beyond dispute. What is secure is the Germanic set and the Old English word. Even the Old English vowel is a small quarrel: the usual stem is short, but a long by-form has been suggested for metrical reasons in verse, and specialists disagree on where that length would have come from. The English adjective is inherited. The Indo-European sequel is optional and uncertain.
Beauty, weather, complexion, and justice
Weather still shows the oldest useful sense. Fair as opposed to foul meant suitable and agreeable: clear rather than stormy. A fair wind, by the late fourteenth century, was one a ship could use. Visual beauty is equally old in English. Light complexion and light hair, by contrast, are a Middle English development, around 1200, when the form faire could be set against browne. That pairing reflects period taste in appearance, not a separate etymology.
The moral and legal family grew beside the aesthetic one. Early in the thirteenth century the adjective could mean in line with propriety; by the mid-fourteenth it was carrying equitable, impartial, free from bias. From that branch come later English specialties. Fair play is recorded in the 1590s and was not first a sports term; an older use around 1300 had meant pleasant amusement, with foul play as sinful pastime. Fair and square appears around 1600. Sporting jargon such as a fair ball or fair catch is dated to the 1850s. Fair game, from hunting, is eighteenth-century. Fair-weather friend is documented from a letter of Alexander Pope written in 1730 and published in 1736. Using fair as a noun for a woman is now archaic.
A quieter shift produced the school-report sense: not excellent, only adequate. From about 1300 the adjective could mean considerable or above average; by 1860 it also meant comparatively good. Fair-to-middling began in livestock markets around 1829. Related technical senses kept the idea of evenness without moral weight: a fair copy is a clean one; a fair hand is legible; in shipbuilding and later in engineering, to fair a surface is to make it smooth and continuous. Those uses still echo “fitting” more than “just.”
The market that began as a holiday
The origin of the word fair as a gathering is a different path. In the early fourteenth century English took the noun from Anglo-French feyre, itself from Old French feire or faire (modern French foire). Behind the French sits Late or Vulgar Latin feria, from classical Latin feriae, religious festivals and holidays, a relative of festus and of English feast. Periodic markets clustered on holy days; the holiday name stuck to the trade. Historical dictionaries treat this noun as Middle English, from the fourteenth century, in the sense of a stated meeting to buy and sell.
Later English stretched that meeting into county fairs, charity bazaars, book and job fairs, and travelling amusement grounds. Romance cognates make the split obvious: French foire, Spanish feria, Italian fiera, Portuguese feira. None of those is the sibling of Swedish fager. The two English words met only in spelling.
What Gothic still shows
If one detail is worth keeping, it is Gothic fagrs. Speakers now reach first for justice, for light hair, or for a carnival on the green, but the Germanic adjective started closer to fitting. Beauty, clear weather, honest dealing, and even only fair as a grade are later English specializations of that older sense of what sits well. The book fair and the funfair are another arrival, borrowed from a Latin holiday. Same letters, two entries into the language.