WordNet (r) 3.0 (2006):

water vapor
    n 1: water in a vaporous form diffused in the atmosphere but
         below boiling temperature [syn: water vapor, water
         vapour]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "water vapor":
   afterdamp, agua, aqua, blackdamp, breath, chokedamp, cloud, damp,
   drinking water, eau, effluvium, exhalation, fetid air, firedamp,
   flatus, fluid, fume, ground water, hard water, head, heavy water,
   hydrol, hydrometeor, hydrosphere, limewater, malaria, mephitis,
   miasma, mineral water, puff of smoke, rain, rainwater, reek,
   salt water, sea water, smoke, smudge, soft water, spring water,
   steam, vapor, volatile, water, well water, wetting agent,
   wetting-out agent