Gwyllion or gwyllon (plural noun from the singular Gwyll or (Yr) Wyll "twilight, loaming") is a Welsh word with a wide range of possible meanings including "ghosts, spirits," "night-wanderers (human or supernatural) up to no good, outlaws of the wild" etc. Gwyllion is only one of a number of words with these or similar meanings in Welsh. It is a comparatively recent word coined inadvertently in the 17th century by the Welsh lexigographer Dr John Davies .Geiriadur Prifysgol Cymru, vol. I, gwyllon