An Etymological Dictionary of the German Language/flennen

by Friedrich Kluge

flennen, vb., ‘to weep ruefully, grin,’ from MidHG. *vlennen; akin to OHG. flannên, ‘to make a wry face,’ from pre-Teut. *flaznan?. Root flas, from pre-Teut. plos, in Lat. plôrare, ‘to weep’?.