From Greek 'Keltoi,' Herodotus's name for western Europeans — possibly meaning 'hidden ones' or 'warriors.'
A branch of the Indo-European language family that includes Irish, Welsh, Scottish Gaelic, Breton, Cornish, and Manx; also used as an adjective for the peoples, cultures, and languages of this group.
From Latin 'Celtae,' from Greek 'Keltoí' (Κελτοί), the name Herodotus and other Greek writers used for the peoples of western and central Europe. The Greek term is first attested in Herodotus (c. 450 BCE), who placed the Keltoi at the source of the Danube and beyond the Pillars of Heracles. The origin of the name is uncertain: it may derive from a Celtic self-designation related to Proto-Celtic *keltos (hidden one, or warrior), or from a PIE root *kel- (to hide, to conceal) — possibly referring to forest-dwelling peoples. Another proposal connects it to
The pronunciation of 'Celtic' with a hard /k/ is the historically older form, reflecting the Greek 'Κελτοί.' The soft /s/ pronunciation (as in the Boston Celtics) arose in the seventeenth century by analogy with other 'ce-' words in English. Among linguists and historians, /ˈkɛl.tɪk/ is standard; in American sports, /ˈsɛl.tɪk/ prevails — a rare case where athletic tradition and academic tradition permanently disagree.