An Etymological Dictionary of the German Language/schleunig

by Friedrich Kluge

schleunig, adj., ‘hasty, speedy,’ from MidHG. sliunec, OHG. slûnîg, ‘quick, speedy,’ in OHG. also ‘thriving.’ A lengthened form of Goth. *slû-na-, for which we have, however, snû-na-; the l seems to have been produced by assimilation on account of the suffix n. Allied to the OTeut. root