An Etymological Dictionary of the German Language/nieder
nieder, adv., from the equiv. MidHG. nider, OHG. nidar, adv., ‘down, downward’; corresponding to OSax. nithar, Du. neder, AS. niþer, E. nether, OIc. niðr; Goth. *niþar, is by chance not recorded. A derivative of the Aryan verbal particle ni, ‘down’ (see Nest), which is preserved in other Teut. forms (see nied and nieden); comp. OSlov. nizŭ, ‘below,’ as well as Sans. ni, ‘down,’ and Sans. nitarâm, which is closely allied to the Teut. adv. — nieder, as an adj., ‘nether, lower, base,’ has been recently formed from the adv. OHG. nidari, MidHG. nider, nidere, adj., ‘nether, low’; akin to OSax. nithiri.