An Etymological Dictionary of the German Language/Annotated/flackern
flackern, verb, ‘to flare, flicker,’ from Middle High German vlackern, ‘to flicker,’ Old High German (once) flagarôn (for flaggarôn?), ‘to fly, flutter about’; akin to Anglo-Saxon flacor, ‘flying, fluttering,’ Middle English flakeren, ‘to fly, flutter about,’ Middle Dutch flackeren, Scandinavian flökra, verb, ‘to flutter,’ as well as the equivalent flökta. Compare the cognate stems Anglo-Saxon flicorian, English to flicker, Dutch flikkern, ‘to glimmer, gleam’; this class, on account of the numerous words it comprised at an early period, cannot be derived from Latin flagrare, nor even be connected with fliegen, to which Old High German flogarôn, flokrôn, ‘to flutter,’ and flogezen, Middle High German vlokzen, ‘to flutter, gleam,’ may be referred.