It's interesting that the two words should have grown to have such a distinction, since they originally meant the same thing, i.e. music of the people, which is pop(ular) from Latin and folk (volk) from German. And from Greek we have lay (laiko) music -- the music of the people, as opposed to the music of the church or the clergy. There may be others, borrowed from other languages, but those are all that I can think of offhand.