An Etymological Dictionary of the German Language/Natter
Natter, f., ‘adder, viper, asp,’ from the equiv. MidHG. nâter, nâtere, OHG. nâtara, f.; corresponding to OSax. nâdra, Du. adder (for nadder; see under Nabe, Näber), AS. nœ̂ddre, E. adder (likewise, with the loss of the initial n, see Otter). Goth. *nêdro is wanting, the graded form nadrs, m., ‘adder,’ being used; OIc. naðr, naðra, ‘adder.’ A specifically Teut. word, the early history of which is not quite clear; it can scarcely be connected with Lat. natrix, ‘water-snake,’ which belongs to nare, natare, ‘to swim.’