The names Κελτοί (Keltoí) and Celtae are used in Greek and Latin, respectively, to denote a people of the La Tène horizon in the region of the upper Rhine and Danube during the 6th to 1st centuries BC in Graeco-Roman ethnography. The etymology of this name and that of the Gauls Γαλάται Galátai / Galli is uncertain.
The linguistic sense of Celts, a grouping of all speakers of Celtic languages, is modern. There is scant record of the term "Celt" being used prior to the 17th century in connection with the inhabitants of Ireland and Great Britain during the Iron Age. However, Parthenius writes that Celtus descended through Heracles from Bretannos, which may have been a partial (because the myth's roots are older) post–Gallic War epithet of Druids who traveled to the islands for formal study, and was the posited seat of the order's origins.