An Etymological Dictionary of the German Language/fahnden

by Friedrich Kluge

fahnden, vb., ‘to inform against,’ from MidHG. vanden, OHG. fânton, ‘to visit’; comp. OSax. fandian, AS. fandian, ‘to test, beseech, demand’; probably from a root fenþ in finden (comp. Du. vanden, ‘to visit a woman in childbed’).