An Etymological Dictionary of the German Language/lachen
lachen, vb., ‘to laugh,’ from the equiv. MidHG. lachen, OHG. lahhên, lahhan, earlier hlahhan; the hk of the HG. is due, according to Goth. hlahjan (pret. hlôh), ‘to laugh,’ to an older hj, AS. hlyhhan, E. to laugh, and the equiv. Du. lachen. In the non-Teut. languages the stem hlah, pre-Teut. klak (probably onomatopoetic, like the cognates of klingen or Lith. klegĕti, ‘to be noisy, laugh loudly’), is not positively authenticated. — Derivative Lache, f., ‘laugh,’ from MidHG. lache, f., ‘laughing,’ comp. E. laughter, AS. hleahtor, MidHG. lahter, ‘laughter.’ Lächeln, vb. ‘to smile,’ from MidHG. lęcheln, is a frequentative of lachen.