An Etymological Dictionary of the German Language/Annotated/Ruhr
Ruhr, feminine, ‘stir, disorder, diarrhœa, dysentery,’ from the equivalent Middle High German ruor, ruore, feminine, literally ‘violent, hasty motion’; allied to rühren; compare Middle High German ruortranc, ‘purgative.’ The general meaning ‘‘violent motion’ is still preserved in the compound Aufruhr, ‘riot.’