Pronunciation: (nī'tru-jun),[key] —n.Chem. a colorless, odorless, gaseous element that constitutes about four-fifths of the volume of the atmosphere and is present in combined form in animal and vegetable tissues, esp. in proteins: used chiefly in the manufacture of ammonia, nitric acid, cyanide, explosives, fertilizer, dyes, as a cooling agent, etc. Symbol: N; at. wt.: 14.0067; at. no.: 7; density: 1.2506 g/l at 0°C and 760 mm pressure.