An Etymological Dictionary of the German Language/Annotated/fahnden

by Friedrich Kluge

fahnden, verb, ‘to inform against,’ from Middle High German vanden, Old High German fânton, ‘to visit’; compare Old Saxon fandian, Anglo-Saxon fandian, ‘to test, beseech, demand’; probably from a root fenþ in finden (compare Dutch vanden, ‘to visit a woman in childbed’).