An Etymological Dictionary of the German Language/Annotated/Ereignis

Ereignis, neuter, ‘event, occurrence,’ for an earlier eröugnis from Middle High German eröugen, Old High German ir-ougen, ‘to show.’ Old High German ougen, Gothic augjan, ‘to show,’ are derivatives of Auge. Hence eröugnis means literally ‘what is shown, what can be seen.’ The spelling Ereignis, found even in the 16th century, was due to the corruption of a word no longer understood.