Surely it was just a translation of the english word "union" or "joint" and the thing about it being an elbow pipe was a false etymology that arose later . Somebody asks Why do they call it a uillean pipe ? and gets told that it's because the instrument is played with the elbow . My Irish is pretty useless but a dictionary gives lots of words that translate "joint" with words that have the ull ,uil as bases. I've just spoken to my local librarian about this who has good Irish . He thinks that I may have a point .