WordNet (r) 3.0 (2006):

rain forest
    n 1: a forest with heavy annual rainfall [syn: rain forest,
         rainforest]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "rain forest":
   afforestation, arboretum, boondocks, bush, bushveld, chase,
   climax forest, cloud forest, dendrology, forest, forest land,
   forest preserve, forestry, fringing forest, gallery forest,
   greenwood, hanger, index forest, jungle, jungles, national forest,
   palmetto barrens, park, park forest, pine barrens, primeval forest,
   protection forest, reforestation, scrub, scrubland,
   selection forest, shrubland, silviculture, sprout forest,
   stand of timber, state forest, timber, timberland, tree veld,
   virgin forest, wildwood, wood, woodland, woods