An Etymological Dictionary of the German Language/lau

by Friedrich Kluge

lau, adj., ‘lukewarm, tepid,’ from the equiv. MidHG. lâ (inflected lâwêr), OHG. lâo (inflected; probably for an earlier *hlâo (Goth. *hlêws); comp. OIc. hlýr, ‘warm, mild,’ Du. lauw. In the non-Teut. languages indubitable cognates are wanting, yet the Rom. cognates of flau (Fr. flou) are derived from OG.