The Collaborative International Dictionary of English v.0.48:

Igloo \Ig"loo\, n.
   1. An Eskimo snow house.
      [1913 Webster]

   2. (Zool.) A cavity, or excavation, made in the snow by a
      seal, over its breathing hole in the ice.
      [1913 Webster]

WordNet (r) 3.0 (2006):

igloo
    n 1: an Eskimo hut; usually built of blocks (of sod or snow) in
         the shape of a dome [syn: igloo, iglu]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "igloo":
   apse, arcade, arcature, arch, arched roof, archway, avalanche,
   blizzard, camber, ceilinged roof, concameration, concha, cove,
   crystal, cupola, dome, driven snow, flake, flurry, geodesic dome,
   granular snow, hogan, jacal, keystone, longhouse, mantle of snow,
   mogul, ogive, skewback, slosh, slush, snow, snow banner, snow bed,
   snow blanket, snow blast, snow fence, snow flurry, snow roller,
   snow slush, snow squall, snow wreath, snow-crystal, snowball,
   snowbank, snowbridge, snowcap, snowdrift, snowfall, snowfield,
   snowflake, snowland, snowman, snowscape, snowshed, snowslide,
   snowslip, snowstorm, span, tepee, tupik, vault, vaulting, voussoir,
   wet snow, wickiup, wigwam