What English uses the name for
In English, Paris is first a place: the capital of France, and by a short step the French government itself. The same spelling is a surname, a given name, and a ready-made label for towns that wanted a European sheen. It is a proper noun, yet once borrowed it behaves like any other English place-word. It forms an ethnic adjective, enters compounds, and lends itself to products whose only remaining link with the Seine is the label.
The origin of the word paris in English is a borrowing, not a native Germanic inheritance. Speakers did not grow it from Old English. They took it from French, as they took so many other continental names that mattered in medieval trade, church, and war.
How the name reached English
Middle English wrote Parys and Paris, following Old French Paris. English evidence from before 1307 already uses the name in a wardrobe account of Edward I. By that date it was also a habitational surname. Later-thirteenth-century rolls list men styled de Paris or de Parys, people from the city or otherwise tied to it. The spelling with y is ordinary Middle English; the modern English form simply settled on i.
The French name is older than Capetian Paris. In the mid first century BCE Julius Caesar recorded the settlement as Lutetia Parisiorum, Lutetia of the Parisii. The Parisii were a Gaulish people on the Seine. Their chief town stood on an island in the river, the later Île de la Cité. Lutetia is usually connected with a Celtic word for mud or marsh, and Latin lutum, dirt or clay, sits beside it: the old compound has been read as the marsh of that people. Late Latin could call the town Parisii as well. In late antiquity the tribal name overtook the marsh name. The community became the civitas of the Parisii; fourth- and fifth-century writers already use forms such as Parisium. By the early Middle Ages the short name Paris was the one in living use. Lutetia survived as an antiquarian or poetic label, and later as a learned joke.
A tribal name that will not sit still
What the Parisii called themselves is not agreed, and the disagreement is worth keeping. One reconstruction starts from Gaulish parios, a cauldron, from Proto-Celtic kʷaryos and a Proto-Indo-European root kʷer-. The Celticist Xavier Delamarre has argued on those lines. Other proposals do not match it. Alfred Holder compared Welsh peryff, lord or commander, and took the people as makers or leaders. Pierre-Yves Lambert tied the first element to an old word for spear and read them as spear people. A traditional story, still advertised by the ship on the city's coat of arms, derives the name from a Celtic word for boat, sometimes set beside Greek baris. That boat account is old and picturesque. It is not the consensus of modern Celtic linguistics, and many handbooks simply mark the tribal name as unknown.
None of those guesses joins the Gauls to the Trojan prince who shares the English spelling. The city-name is a people-name that won out over a marsh-name. The rest is reconstruction, and the reconstructions do not yet converge.
Senses that grew off the map
Once the city-name was English, it spread sideways. Parisian for an inhabitant is the expected derivative. Plaster of Paris, the calcined gypsum that sets hard with water, is on record in English by the early fifteenth century and already appears in Anglo-Norman as plastre de Parys in 1284. The plaster was associated with gypsum beds at Montmartre; the place supplied the material, then the material kept the place. Paris green, a copper-arsenic pigment, is a later industrial coinage of the same type: a product tagged with the capital. North American towns named Paris, from Kentucky and Texas to Ontario, copy the French city; the Ontario community even sits near gypsum used for the plaster. As a given name, Paris is transferred from the place, and in modern English it is used for women as well as men.
English pronunciation kept a final s that standard French no longer sounds, and it kept the stress on the first syllable. The written form looks international. The spoken form is insular.
Two lookalikes that are not this word
Two other English uses look identical and are historically separate. The Trojan Paris is a learned borrowing from Greek Páris, Latin Paris, the son of Priam who takes Helen and brings on the war at Troy. That personal name is probably Anatolian. A Luwian comparison with a Hittite name Parizitis, roughly foremost man, is the leading guess. An old link with Greek pēra, a bag or pouch, is folk etymology. Medieval writers sometimes fused the hero with the French city; the two lines do not meet.
Separately, herb paris, the woodland plant Paris quadrifolia, comes from Medieval Latin herba paris, herb of a pair or of equals, from Latin par, equal. The leaves and floral parts sit in matching fours, which is why herbalists also called it true-love or true lover's knot. Later association tied the plant to the city; the Latin morphology is about pairing, not about the Seine.
A useful last detail sits in a neighbour language rather than in another myth. Dutch has Parijs, Italian has Parigi, and Russian has Parizh, all names of the same city taken from the same medieval French source and then bent by each language's own sound pattern. English kept the consonants of Paris almost intact. What it did not keep is Lutetia, except in the geological Lutetian age, named for rocks of the Paris basin: the marsh-name that the living city discarded.