An Etymological Dictionary of the German Language/Annotated/Gräuel
Gräuel, masculine, from the equivalent Middle High German griul, griuwel, masculine, ‘terror, horror, abomination’ (Dutch gruwel); allied to Modern High German grauen, Middle High German grûwen, ‘to horrify, terrify,’ Old High German ingrûên, ‘to shudder.’ Akin also to Modern High German grausam, from Middle High German grûwesam, ‘exciting terror’; Modern High German gräulich, from Middle High German griuwelich. The root grû, ‘to frighten,’ is wanting in the rest of the Old Teutonic dialects. See Graus.