co

(noun) an odorless very poisonous gas that is a product of incomplete combustion of carbon. Synonyms: carbon monoxide, carbon monoxide gas, CO.

(noun) a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition. Synonyms: cobalt, Co, atomic number 27.

(noun) one who refuses to serve in the armed forces on grounds of conscience. Synonyms: conscientious objector, CO.

(noun) a state in west central United States in the Rocky Mountains. Synonyms: Colorado, Centennial State, CO.