Spaw, words are in the public domain; it doesn't really make sense to say that the word folk was "stolen". A word gets picked up, changed around, added to, and subtracted from, and ultimately emerges in another time and place as something that has echoes of earlier versions, but also reflects the changes that time and lots of handling have brought about. Ironically, it's the same thing that we cherish about folk music; somehow, the hidebound traditionalists among us think it's a good thing when applied to songs, but a bad thing when applied to word definitions that they think should remain frozen in time. Forget about ownership; if that's what you're after, you need to invent a new word and get yourself a copyright or trademark. It's too late to do that with "folk". Anyone who hopes to hang onto a static, unchanging definition of that word is bound to be disappointed.