An Etymological Dictionary of the German Language/Annotated/ahnen
ahnen, verb, ‘to forebode, suspect,’ from Middle High German anen, ‘to foresee, forebode,’ foreign to the older period and to the rest of the Teutonic dialects; it has been connected with the Old Aryan root an, ‘to breathe, respire,’ so that it may be a primitively cognate of ahnden, under the influence of which it also appears in Modern High German as ahnden. It is better, however, to regard it as a derivative of the preposition an; allied, literally ‘to befall, seize, attack' (properly said of ghosts or visions).