The word banshee was first used in the English language in a 1771 book about Scotland, where it was spelled benshi. For the next century or so, all kinds of spellings were attested, such as ben-shie and banshie, but by the late ninetenth century the form banshee was widely accepted. The word is a phonetic transcription of the Irish term bean sidhe, meaning "female elf" or, more literally, "woman of the fairy mound". Bean is from ben, which is from Proto-Celtic bena and Proto-Indo-European gwen, also meaning "woman" (and the root of words as diverse as queen and gynecology). Sidhe is from Proto-Celtic sidos, which could just mean "mound" but definitely still had connotations of fairies, and that derives from Proto-Indo-European sed, "to sit". Usage of the word banshee has been increasing since the 1980s.
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.