The Collaborative International Dictionary of English v.0.48:

Ammoniac \Am*mo"ni*ac\(or Gum ammoniac \Gum` am*mo"ni*ac\, n.
   [L. Ammoniacum, Gr. 'ammoniako`n a resinous gum, said to
   distill from a tree near the temple of Jupiter Ammon; cf. F.
   ammoniac. See Ammonite.] (Med.)
   The concrete juice (gum resin) of an umbelliferous plant, the
   Dorema ammoniacum. It is brought chiefly from Iran in the
   form of yellowish tears, which occur singly, or are
   aggregated into masses. It has a peculiar smell, and a
   nauseous, sweet taste, followed by a bitter one. It is
   inflammable, partially soluble in water and in alcohol, and
   is used in medicine as an expectorant and resolvent, and for
   the formation of certain plasters.
   [1913 Webster + AS]

WordNet (r) 3.0 (2006):

gum ammoniac
    n 1: the aromatic gum of the ammoniac plant [syn: ammoniac,
         gum ammoniac]