WordNet (r) 3.0 (2006):

tropics
    n 1: the part of the Earth's surface between the Tropic of
         Cancer and the Tropic of Capricorn; characterized by a hot
         climate [syn: Torrid Zone, tropical zone, tropics]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "tropics":
   Antarctic Zone, Arctic Circle, Arctic Zone, Frigid Zones,
   Torrid Zone, Tropic of Cancer, Tropic of Capricorn, Variable Zones,
   climate, clime, equator, furnace, hell, horse latitudes, inferno,
   latitude, longitude, longitude in arc, meridian, oven, parallel,
   prime meridian, roaring forties, steam bath, subtropics, the line,
   tropic, zone