An Etymological Dictionary of the German Language/Annotated/rünstig

by Friedrich Kluge

rünstig, adjective, ‘flowing, running,’ in blutrünstig, ‘bleeding, bloody,’ from Middle High German bluot-runsec, -runs, adjective, ‘bloody, wounded,’ allied to Middle High German and Old High German bluot-runs, ‘hæmorrhage, bleeding wound.’ Runs is an abstract from rinnen; compare Gothic runs (genitive runsis), ‘course,’ runs blôþis, ‘issue of blood.’ Hence also Modern High German (dialectic) Runs, ‘course of a torrent.’