Definitions of Co:

noun: one who refuses to serve in the armed forces on grounds of conscience
noun: a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition
noun: a state in west central United States in the Rocky Mountains
noun: an odorless very poisonous gas that is a product of incomplete combustion of carbon
name: A surname (very rare: popularity rank in the U.S.: #47909)