WordNet (r) 3.0 (2006):

sand dune
    n 1: a ridge of sand created by the wind; found in deserts or
         near lakes and oceans [syn: dune, sand dune]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "sand dune":
   anthill, barrow, brae, butte, down, drumlin, dune, fell, foothills,
   hill, hillock, hummock, knob, knoll, molehill, monticle, monticule,
   moor, mound, sand, sand pile, sandbar, swell