- carbon monoxide, carbon monoxide gas, CO - an odorless very poisonous gas that is a product of incomplete combustion of carbon
--1 is a kind of trigonometric function, circular function; monoxide; trigonometric function, circular function; monoxide
- cobalt, Co, atomic number 27 - a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition
--2 is a kind of lettuce; metallic element, metal; lettuce; metallic element, metal
--2 is a substance of smaltite; cobaltite
--2 has particulars: cobalt 60 - conscientious objector, CO - one who refuses to serve in the armed forces on grounds of conscience
--3 is a kind of dissenter, dissident, protester, objector, contestant; dissenter, dissident, protester, objector, contestant
- Colorado, Centennial State, CO - a state in west central United States in the Rocky Mountains
--4 is a kind of American state; American state
--4 is a part of
--4 has parts:United States, United States of America, America, US, U.S., USA, U.S.A.