lowland

from WordNet (r) 3.0 (2006)

lowland
    adj 1: of relatively low or level country [ant: {highland(a)},
           {upland}]
    n 1: low level country [ant: {highland}, {upland}]

from The Collaborative International Dictionary of English v.0.48

Lowland \Low"land\, n.
   Land which is low with respect to the neighboring country; a
   low or level country; -- opposed to {highland}.
   [1913 Webster]

   {The Lowlands}, Belgium and Holland; the Netherlands; also,
      the southern part of Scotland.
      [1913 Webster]

from U.S. Gazetteer (1990)

Lowland, NC
  Zip code(s): 28552
Lowland, TN
  Zip code(s): 37778