An Etymological Dictionary of the German Language/lauter
lauter, adj., ‘pure, mere,’ from MidHG. lûter, adj., ‘bright, pure, clear’ OHG. lûttar, hlûttar. Since Goth. and LG. tr is not permutated in HG. (comp. zittern, Winter, Eiter, Otter, and bitter), Goth. hlûtrs, ‘pure,’ AS. hlûttor, ‘pure, clear’ (wanting in E.), and Du. louter are corresponding forms. A prim. Teut. adj. perhaps orig. signifying ‘washed’ (like Lat. lautus, lit. ‘washed,’ then ‘splendid, magnificent’). This prim. meaning may be assumed since the Teut. root hlût, preserved only in the adj. lauter, is cognate with Gr. κλυδ and κλύζω, ‘to rinse out, wash, cleanse,’ and κλύδων, ‘beating of the waves.’