An Etymological Dictionary of the German Language/Keusch
keusch, adj., ‘chaste, pure,’ from MidHG. kiusche, kiusch, adj., ‘moderate, quiet, modest, bashful'; OHG. chûski, adj., ‘continent, moderate.’ AS. cûse is borrowed from the OSax. of the Heliand, OSax. *kûsci, of which only the corresponding adv. cûsco is recorded; Du. kuisch, ‘cleanly, chaste.’ The prim. meaning of the OTeut. adj., which appears in all these forms, is presumably ‘pure’; comp. Du. kuischen, ‘to clean, purify’; OHG. unchûskî, ‘dirt’ (also Hess. unkeuscher Weg, ‘road in bad condition’). —