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)