carbon monoxide vs carbon monoxide gas

carbon monoxide and carbon monoxide gas both are nouns.

Word	Noun	Adjective	Verb	Adverb
carbon monoxide	Yes	No	No	No
carbon monoxide gas	Yes	No	No	No

As nouns, carbon monoxide and carbon monoxide gas are synonyms defined as:

carbon monoxide and carbon monoxide gas: an odorless very poisonous gas that is a product of incomplete combustion of carbon

Other synonyms of carbon monoxide include CO.

carbon monoxide (noun)	carbon monoxide gas (noun)
an odorless very poisonous gas that is a product of incomplete combustion of carbon	an odorless very poisonous gas that is a product of incomplete combustion of carbon