A settlement that began as a yard
In modern English a town is a populated place with streets, shops, and some form of local government, usually larger than a village and smaller than a city. Speakers stretch the word without much fuss. A huge city can be called a big town. In parts of the United States the same noun names a township. In older British use it could mean a rural settlement that held a regular market. Going into town often means heading for the nearest cluster of shops, whether or not the place would satisfy a planner’s definition. That urban sense is the latecomer. For most of its life in English the word sat closer to a yard, a farm, or an enclosed plot than to a high street.
The origin of the word town is not a later French or Latin import. It is native English, inherited from Old English tūn, already current before 1150. What changed is not the pedigree of the noun but the kind of place it was allowed to name.
Old English tūn
Old English tūn covered a tight cluster of related ideas: an enclosed piece of ground, a garden or field, a yard, a farm or manor, a homestead, a dwelling. Later in the Old English period it could already mean a group of houses or a village. The word belonged to ordinary rural vocabulary. When speakers needed a term for a walled or Roman-style urban centre they more often reached for burh, the ancestor of borough, or for the Latin loan ceaster, the source of the -chester and -caster endings in English place names.
Middle English spelled the word toun, with a crowd of local variants. By then the meaning had begun to tilt toward a populated place with some local government, often with defences. Early texts do not always separate a municipality from a hamlet, and both senses sit in the same word. After the Norman Conquest, English used toun as a working counterpart to French ville. From about the mid-twelfth century the sense of a collection of houses larger than a village is in place. In medieval England the typical association was a cluster of houses tied to a market. That market link still survives in the historical British sense of a country settlement that held a weekly market.
A Germanic noun beside a Celtic fort
Behind Old English tūn stands Proto-West Germanic tūn and Proto-Germanic tūną, reconstructed as an enclosure or fortified place. Most etymological handbooks treat this Germanic form as an early borrowing from Proto-Celtic dūnom, a stronghold or rampart. The timing is part of the argument: the loan is usually placed before Grimm’s law turned a Celtic d into a Germanic t. If that account is right, English town is a distant relative of Irish dún, fortress, and of Welsh din, with its later derivative dinas, city. It is also a doublet of English dun in the Celtic sense of a fort. The same Celtic word is the -dunum of Gaulish names later Latinized across Roman Gaul.
Not every authority tells the story as a borrowing. The Oxford English Dictionary records the Germanic base as either cognate with or borrowed from the Celtic one, and it leaves the further Indo-European source disputed. One proposal links the form to an enclosed or fortified place, sometimes tied to a verb meaning to close. Another reconstructs a word for something lasting or durable. Those deeper roots are not settled, and it is better to leave them open than to invent a single ancestor.
What is not in doubt is the family of Germanic descendants, and they still show the older meaning. Dutch tuin is a garden. German Zaun is a fence. Old Norse tún, with descendants in Norwegian, Swedish, and Danish tun, is a farmyard or enclosed plot. Frisian tún and related Low German forms keep the garden or fence sense. West Germanic languages often named the barrier; North Germanic ones more often named the yard inside it. Old English is slightly odd in that the noun is not clearly attested as fence, though a related verb tȳnan meant to enclose, and compounds about fencing fields exist. From Germanic the word also passed into Slavic, where Russian tyn and related forms mean a fence or stockade.
How an enclosure became urban
The English semantic path is unusually long. Other Germanic languages stayed with the fence, the hedge, or the garden. English kept the enclosed space, then the farm, then the cluster of houses, then the market settlement, then the urban place set against the country. As burh and ceaster thinned out in early Middle English, town, not the French loan city, became the default word for an urban settlement in general. City kept a higher or more legal flavour. Town became the everyday opposite of country.
The same Old English noun is fossilized in hundreds of English place names as -ton: Southampton, Brighton, Preston, and many others. Those names usually point to a farm, estate, or enclosed settlement, not to a later municipal borough. In American usage the word often means a township, a civil unit rather than a dense core. Figurative uses piled up later. In town and out of town are recorded from the fourteenth century. On the town, for fashionable living, appears in the early eighteenth. Man about town follows in the 1730s. Go to town, meaning to do something with energy, is only twentieth-century slang. Town versus gown still names the split between local residents and a university.
Obsolete senses have not vanished so much as they have been boxed away. Dictionaries still record the old meaning of an enclosure around a manor house, and in some British and Scottish dialects the word once meant a farm or farmyard. Those uses make the modern urban reading look sudden only if the intervening centuries are skipped.
What the cognates still remember
If you want a single picture of the history, look at German Zaun. The German speaker’s fence and the English speaker’s high street are the same word, split by a long shift that English almost uniquely allowed. Irish dún still names a fort, which is closer to the Celtic starting point than either the German fence or the English street grid. The English word moved from the palisade to the plot, from the plot to the farm, and from the farm to the place you mean when you say you are going into town.