Uncertain. The term is thought to have existed as Vulgar Latin *lausa (whence Old French lose, Old Occitan lausa), possibly ultimately borrowed from Gaulish *lausā, from Proto-Celtic *lausā (“stone”), from Proto-Indo-European *léh₁u-s ~ *l̥h₁w-és, whence also Proto-Celtic *līwos (“stone”), from *leh₁- (“stone”).