An Etymological Dictionary of the German Language/Annotated/warnen

by Friedrich Kluge

warnen, verb, ‘to warn, admonish,’ from Middle High German warnen, ‘to watch over, protect,’ Old High German warnen (węrnen), ‘to deny, refuse, decline.’ Corresponding to Old Saxon węrnian, ‘to decline, withhold.’ Anglo-Saxon wyrnan, English warn, Old Icelandic varna, ‘to refuse.’ On account of the meaning the connection with Old High German warnôn (see wahren) is dubious; undoubted cognates have not yet been found.