Source : Webster's Revised Unabridged Dictionary (1913)

Nether \Neth"er\, a. [OE. nethere, neithere, AS. ni?era, fr. the
   adv. ni?er downward; akin to neo?an below, beneath, D. neder
   down, G. nieder, Sw. nedre below, nether, a. & adv., and also
   to Skr. ni down. [root]201. Cf. {Beneath}.]
   Situated down or below; lying beneath, or in the lower part;
   having a lower position; belonging to the region below;
   lower; under; -- opposed to {upper}.

         'Twixt upper, nether, and surrounding fires. --Milton.

         This darksome nether world her light Doth dim with
         horror and deformity.                    --Spenser.

         All my nether shape thus grew transformed. --Milton.

Source : WordNet®

nether
     adj 1: lower; "gnawed his nether lip"
     2: of the underworld; "nether regions" [syn: {chthonian}, {chthonic},
         {lower}]
     3: located below or beneath something else; "nether garments";
        "the under parts of a machine" [syn: {under}]