An Etymological Dictionary of the German Language/Annotated/Flocke
Flocke, feminine, ‘flake, flock (of wool), flue,’ from Middle High German vlocke, masculine, ‘flake, snowflake,’ Old High German floccho; compare Dutch vlok, Danish flokke, Swedish flokka, English (not in Anglo-Saxon) flock, but Old Icelandic flóke, ‘flock (of hair, wool, &c.).’ The supposition that the word was borrowed from Latin floccus is hardly worth considering, since the High German word is recorded even in the Old High German period, and gives no support to such a derivation (yet compare Flaum). Besides many possible roots exist within the Teutonic group, either in fliegen (Teutonic root flugh, from pre-Teutonic plugh) or in Anglo-Saxon flacor, ‘flying’ (see flackern); on account of Old Icelandic flóke, the latter is to be preferred. English flock, ‘herd,’ is beside the mark; like Old Icelandic flokkr, ‘herd, flock,’ and Anglo-Saxon flocc, it almost certainly belongs to fliegen, and probably signified originally ‘a swarm of flying creatures’ (Kette, ‘covey,’ on the other hand, meant properly ‘any kind of herd’).