An Etymological Dictionary of the German Language/ungeheuer
Appearance
ungeheuer, adj., ‘monstrous, atrocious,’ from MidHG. ungehiure, OHG. ungihiuri, ‘uncanny, frightful’; allied to Angeheuer, n., ‘monster,’ from MidHG. ungehiure, ‘savage, dragon, ghostly creature,’ OHG. ungihiurì, ‘monster.’ See geheuer.