An Etymological Dictionary of the German Language/nüchtern
nüchtern, adj., from the equiv. MidHG. nüchtern, nüchter, OHG. nuohturn, nuohtarnîn, adj., ‘without food or drink, fasting, temperate,’ comp. Du. nuchter, AS. nixtnig. The assumption that the word is based on Lat. nocturnus does not suffice to explain the meaning of nüchtern, since the Lat. term signifies only ‘nocturnal, at night’; nor is it possible to regard OHG. nuohturn as a genuine Teut. derivative of Aryan nō̆kt, ‘night’ (OIc. nótt), since it must have been equiv. in meaning to Lat. nocturnus. It may more probably be compared with Gr. νηφάλιος, ‘I am sober,’ νηφάλιος, νήπτης, ‘sober, without wine,’ the φ-π of which may represent an old guttural. In spite of this probable connection of the root, the suffix of nüchtern is still obscure,