The Collaborative International Dictionary of English v.0.48:

ammonia \am*mo"ni*a\ ([a^]m*m[=o]"n[i^]*[.a]), n. [From sal
   ammoniac, which was first obtaining near the temple of
   Jupiter Ammon, by burning camel's dung. See Ammoniac.]
   (Chem.)
   A gaseous compound of hydrogen and nitrogen, NH3, with a
   pungent smell and taste: -- often called volatile alkali,
   and spirits of hartshorn. It is very soluble in water,
   forming a moderately alkaline solution, and is used in
   aqueous solution as a household cleaning agent, such as for
   cleaning grease from glass.
   [1913 Webster + PJC] Ammoniac

WordNet (r) 3.0 (2006):

ammonia
    n 1: a water solution of ammonia [syn: ammonia water,
         ammonia, ammonium hydroxide]
    2: a pungent gas compounded of nitrogen and hydrogen (NH3)

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "ammonia":
   Dry Ice, Freon, acetylene, argon, asphyxiating gas, butane,
   carbon dioxide, carbon monoxide, castor-bean meal, chlorine,
   coal gas, commercial fertilizer, compost, coolant, dressing, dung,
   enrichener, ethane, ether, ethyl chloride, ethylene, fertilizer,
   fluorine, formaldehyde, freezing mixture, guano, helium, hydrogen,
   ice, ice cubes, illuminating gas, krypton, lewisite, liquid air,
   liquid helium, liquid oxygen, manure, marsh gas, methane, muck,
   mustard gas, natural gas, neon, night soil, nitrate, nitrogen,
   organic fertilizer, oxygen, ozone, phosphate, poison gas, propane,
   radon, refrigerant, sewer gas, superphosphate, xenon