Origin and history of Eton

the usual Old English word for "river, running water" (still in use in Lancashire, according to OED), from Proto-Germanic *ahwo- (source also of Old Frisian a, Old Saxon aha, Old High German aha, German ahe-, Old Dutch aha, Old Norse "water"), from PIE root *ekweh- "water" (see aqua-). "The standard word in place-names for river denoting a watercourse of greater size than a broc or a burna" [Cambridge Dictionary of English Place-Names].

Middle English toun, "inhabited place having some degree of local government," from Old English tun "enclosure, garden, field, yard; farm, manor; homestead, dwelling house, mansion;" later "group of houses, village, farm," from Proto-Germanic *tunaz, *tunan "fortified place" (source also of Old Saxon, Old Norse, Old Frisian tun "fence, hedge," Middle Dutch tuun "fence," Dutch tuin "garden," Old High German zun, German Zaun "fence, hedge").

This was an early Germanic borrowing from Celtic *dunon "hill, hill-fort" (source also of Old Irish dun, Welsh din "fortress, fortified place, camp," dinas "city," Gaulish-Latin -dunum in place names). It is reconstructed to be from PIE *dhu-no- "enclosed, fortified place, hill-fort," from root *dheue- "to close, finish, come full circle" (see down (n.2)).

The meaning "collection of houses larger than a village" (mid-12c.) arose after the Norman conquest from the use of this word to correspond to French ville. In medieval England the sense tended toward "large number of houses associated with a market." In U.S. it is often used in the meaning "township."

The modern word is partially a generic term, applicable to cities of great size as well as places intermediate between a city and a village; such use is unusual, the only parallel is perhaps Latin oppidium, which occasionally was applied even to Rome or Athens (each of which was more properly an urbs).

From Middle English, typically figurative of a place of sophistication. The game of town ball, an early version of baseball, is recorded by that name from 1852. A town car (1907) originally was a motor car with an enclosed passenger compartment and open driver's seat.

To be in town or out of town is from 14c. On the town (or upon the town) "living the high life, in the fashionable swing of things" is attested from 1712. Man about town "one constantly seen at public and private functions" is attested from 1734. Colloquial go to town "do (something) energetically" is recorded by 1933. 

Town-crier is attested from c. 1600; town-talk "common talk of a town, a subject of gossip" is by 1650s; town clock is by 1466 (in reference to Dublin).