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1771, from phonetic spelling of Irish bean sidhe "female of the Elves," from bean "woman" (from PIE *gwen-; see queen) + sidhe, from sith "fairy" or sid "fairy mound." Specifically, one who calls to the spirits of the dead.
(("woman of the fairies") supernatural being in Irish and other Celtic folklore whose mournful "keening," or wailing screaming or lamentation, at night was believed to foretell the death of a member of the family of the person who heard the spirit. In Ireland banshees were believed to warn only families of pure Irish descent. The Welsh counterpart, the gwrach y Rhibyn ("witch of Rhibyn"), visited only families of old Welsh stock