The Celts (/ k ɛ l t s, s ɛ l t s /, see pronunciation of Celt for different usages) were an Indo-European people in Iron Age and Medieval Europe who spoke Celtic. Celtic definition, a branch of the Indo-European family of languages, including especially Irish, Scottish Gaelic, Welsh, and Breton, which survive now in Ireland. Define Celtic. Celtic synonyms, Celtic pronunciation, Celtic translation, English dictionary definition of Celtic. also Kelt·ic n. A subfamily of the Indo-European. The official site of the Boston Celtics. Includes news, scores, schedules, statistics, photos and video. Celtic symbols and Celtic signs hold tremendous meaning and power. Discover the rich realm of Celtic symbol meanings on whats-your-sign.com The home of Celtic Football on BBC Sport online. Includes the latest news stories, results, fixtures, video and audio.