Noun co has 4 senses

• co(n = noun.substance) carbon monoxide, carbon monoxide gas - an odorless very poisonous gas that is a product of incomplete combustion of carbon; Array
is a kind of monoxide

• co(n = noun.substance) atomic number 27, cobalt - a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition; Array
is a kind of metal, metallic element
has particulars: cobalt 60

• co(n = noun.person) conscientious objector - one who refuses to serve in the armed forces on grounds of conscience; Array
is a kind of contestant, dissenter, dissident, objector, protester

• co(n = noun.location) centennial state, colorado - a state in west central United States in the Rocky Mountains; Array
has parts: mesa verde national park, rocky mountain national park, boulder, colorado springs, capital of colorado, denver, mile-high city, pueblo, arkansas, arkansas river, colorado, colorado river, colorado plateau, north platte, north platte river, pike's peak, republican, republican river, san juan mountains, mount sherman, sherman, south platte, south platte river
is a kind of american state
is a part of america, the states, u.s., u.s.a., united states, united states of america, us, usa