'Cyanogen' definitions:

Definition of 'cyanogen'

noun

A colorless toxic gas with a pungent almond odor; has been used in chemical warfare

From: GCIDE

Cyanogen \Cy*an"o*gen\ (s?-?n"?-j?n), n. [Gr. ky`anos a dark blue substance + -gen: cf. F. cyanog[`e]ne. So called because it produced blue dyes.] (Chem.) A colorless, inflammable, poisonous gas, C2N2, with a peach-blossom odor, so called from its tendency to form blue compounds; obtained by heating ammonium oxalate, mercuric cyanide, etc. It is obtained in combination, forming an alkaline cyanide when nitrogen or a nitrogenous compound is strongly ignited with carbon and soda or potash. It conducts itself like a member of the halogen group of elements, and shows a tendency to form complex compounds. The name is also applied to the univalent radical, CN (the half molecule of cyanogen proper), which was one of the first compound radicals recognized. [1913 Webster]
Note: Cyanogen is found in the commercial substances, potassium cyanide, or prussiate of potash, yellow prussiate of potash, Prussian blue, Turnbull's blue, prussic acid, etc. [1913 Webster]