An Etymological Dictionary of the German Language/flackern
flackern, vb., ‘to flare, flicker,’ from MidHG. vlackern, ‘to flicker,’ OHG. (once) flagarôn (for flaggarôn?), ‘to fly, flutter about’; akin to AS. flacor, ‘flying, fluttering,’ MidE. flakeren, ‘to fly, flutter about,’ MidDu. flackeren, Scand. flökra, vb., ‘to flutter,’ as well as the equiv. flökta. Comp. the cognate stems AS. flicorian, E. to flicker, Du. flikkern, ‘to glimmer, gleam’; this class, on account of the numerous words it comprised at an early period, cannot be derived from Lat. flagrare, nor even be connected with fliegen, to which OHG. flogarôn, flokrôn, ‘to flutter,’ and flogezen, MidHG. vlokzen, ‘to flutter, gleam,’ may be referred.