An Etymological Dictionary of the German Language/Annotated/Sündflut
Sündflut, feminine, ‘the Flood,’ is an early Modern High German corruption of the equivalent Middle High German and Old High German sin-vluot, which means literally ‘great universal overflow.’ The term sin-, which appears only in Old Teutonic compounds, signifies ‘general, constantly, always’ (compare Singrün, ‘periwinkle’), in Gothic sinteins, ‘daily, everlasting,’ Anglo-Saxon symble, Old Saxon and Old High German simblum, ‘always.’ Compare Latin sem-per, ‘always.’