Webster's English Dictionary

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ammoniac

am.mo.ni.ac \*-'mo--ne--.ak\ n [ME & L; ME, fr. L ammoniacum, fr. Gk 
   ammo-niakon, fr. neut. of]ammo-niakos of Ammon : the aromatic gum resin of 
   a Persian herb (Dorema ammoniacum) of th e carrot family used as an 
   expectorant and stimulant and in plasters