An Etymological Dictionary of the German Language/Schlüssel

by Friedrich Kluge

Schlüssel, m., ‘key,’ from the equiv. MidHG. slüȥȥel, OHG. sluȥȥil, m.; corresponding to OSax. slutil, Du. sleutel. This derivative of schließen (Goth. *slutila-) is wanting in E., OIc., and Goth.