An Etymological Dictionary of the German Language/Lauge
Lauge, f., ‘lye,’ from the equiv. MidHG. louge, OHG. louga, f.; corresponding to MidLG. lôge, Du. loog, AS. leáh, and the equiv. E. lye. In OIc. laug, f., means ‘warm bath’ (preserved in ModIc. in numerous proper names, and signifying ‘hot spring’). Perhaps this Teut. word for ‘warm bath’ is connected with the Aryan root, low, lu, ‘to bathe’ (comp. Lat. lavâre), like the equiv. Swed. lut, of which an extended Aryan luk, equiv. to Teut. luh, ‘to wash,’ may appear in OHG. luhhen, ‘to wash,’ Suab. lichen, North Franc. and Henneberg lüen, ‘to rinse washed linen.’ The HG. word occurs in the Slav. languages as lug, ‘lye.’