cyanogenyoudaoicibaDictYouDict
"A colourless flammable highly poisonous gas made by oxidizing hydrogen cyanide", Early 19th century: from French cyanogène, from Greek kuanos 'dark blue mineral' + -gène (see -gen), so named because it is a constituent of Prussian blue.
phosgeneyoudaoicibaDictYouDict
"A colourless poisonous gas made by the reaction of chlorine and carbon dioxide. It was used as a poison gas, notably in the First World War", Early 19th century: from Greek phōs 'light' + -gen, with reference to its original production by the action of sunlight on chlorine and carbon monoxide.