Accodring to New World Celts, The origin of the word Celt is from the Latin celtae, and refers to, according to Webster,
"a member of a division of the early Indo-European peoples in Iron-Age and pre-Roman Europe distributed from the British Isles and Spain to Asia Minor and in part absorbed into the Roman Empire as Britons, Gauls, Boii, Galatians, or Celtiberians."
OR
"a descendant of these people who has somewhere in his background a native knowledge of the Celtic language."
OR
"a modern Gael, Highland Scot, Irishman, Welshman, Cornishman or Breton."