Dacian 'deish@n is an extinct language, generally believed to be a member of the Indo-European family, that was spoken in the Carpathian region in antiquity.
In the 1st century, it was probably the predominant language of the ancient regions of Dacia and Moesia and possibly of some surrounding regions.
The language was extinct by the 4th century AD.
While there is general agreement among scholars that Dacian was an Indo-European language, there are divergent opinions about its place within the IE family:
Dacian was a dialect of the extinct Thracian language, or vice versa, e. g . and .
Dacian was a language distinct from Thracian but closely related to it, belonging to the same branch of the Indo-European family (a "Thraco-Dacian", or "Daco-Thracian" branch has been theorised by some linguists).
Dacian, Thracian, the Baltic languages (Duridanov also adds Pelasgian) formed a distinct branch of Indo-European, e.g. Schall (1974), Duridanov (1976), Radulescu (1987) and Mayer (1996).
Daco-Moesian was the ancestor of Albanian, belonging to a branch other than Thracian, but closely related to Thracian and distinct from Illyrian. This is a theory proposed by Georgiev (1977).
The Dacian language is poorly documented. Unlike Phrygian, which is documented by c. 200 inscriptions, only one Dacian inscription is believed to have survived. The Dacian names for a number of medicinal plants and herbs may survive in ancient literary texts, including about 60 plant-names in Dioscorides. About 1,150 personal names and 900 toponyms may also be of Dacian origin. A few hundred words in modern Romanian and Albanian may have originated in ancient Balkan languages such as Dacian (see List of Romanian words of possible Dacian origin). Linguists have reconstructed about 100 Dacian words from placenames using established techniques of comparative linguistics, although only 20–25 such reconstructions had achieved wide acceptance by 1982.
There is scholarly consensus that Dacian was a member of the Indo-European family of languages.