On the site of the city was a pre-Roman settlement named Napoca. After the AD 106 Roman conquest of the area, the place was known as Municipium Aelium Hadrianum Napoca. Possible etymologies for Napoca or Napuca include the names of some Dacian tribes such as the Naparis or Napaei, the Greek term napos (νάπος), meaning “timbered valley” or the Indo-European root *snā-p- (Pokorny 971-2), “to flow, to swim, damp”.
The first written mention of the city’s current name – as a Royal Borough – was in 1213 under the Medieval Latin name Castrum Clus. Despite the fact that Clus as a county name was recorded in the 1173 document Thomas comes Clusiensis, it is believed that the county’s designation derives from the name of the castrum, which might have existed prior to its first mention in 1213, and not vice versa. With respect to the name of this camp, it is widely accepted as a derivation from the Latin term clausa – clusa, meaning “closed place”, “strait”, “ravine”. Similar senses are attributed to the Slavic term kluč, meaning “a key“ and the German Klause – Kluse (meaning “mountain pass” or “weir“). The Latin and Slavic names have been attributed to the valley that narrows or closes between hills just to the west of Cluj-Mănăştur. An alternative hypothesis relates the name of the city to its first magistrate, Miklus – Miklós / Kolos.
The Hungarian form, first recorded in 1246 as Kulusuar, underwent various phonetic changes over the years (uar/vár means “castle” in Hungarian); the variant Koloswar first appears in a document from 1332. Its Saxon name Clusenburg/Clusenbvrg appeared in 1348, but from 1408 the form Clausenburg was used. The Romanian name of the city used to be spelled alternately as Cluj or Cluş, the latter being the case in Mihai Eminescu‘s Poesis. In 1974, the Romanian Communist authorities added “-Napoca” back to the city’s name as a nationalist gesture, emphasising its pre-Roman roots. The full name is rarely used outside of official contexts. In Yiddish it is known as קלאזין (Klazin) or קלויזענבורג (Kloyznburg).