An Etymological Dictionary of the German Language/Donner
Donner, m., ‘thunder,’ from the equiv. MidHG. doner, OHG. donar, m., corresponding to AS. þunor, E. thunder; Goth. *þunara-, m. It is the OTeut. name for thunder, under which also the weather-god was worshipped (see Donnerstag). The name comes from the Aryan root ten, discussed under dehnen, Dohne, and dünn. In its application to sound we meet with this root in Gr. τόνος, ‘string, rope, stretching, tone, accent,’ Sans. root tan, ‘to resound, roar, tanayitnú-s, ‘roaring, thundering,’ Lat. tonare (AS. þunian, Goth. *þunôn, ‘to thunder’), Lat. tonitrus; the latter correspondences are, on account of their meaning, the most closely allied to the Teut. words.