denim vs jeans

denim and jeans both are nouns.

Word	Noun	Adjective	Verb	Adverb
denim	Yes	No	No	No
jeans	Yes	No	No	No

As nouns, denim and jeans are synonyms defined as:

denim and jeans: (used in the plural) close-fitting trousers of heavy denim for manual work or casual wear

Other synonyms of denim include blue jeans.

denim (noun)	jeans (noun)
a coarse durable twill-weave cotton fabric	(used in the plural) close-fitting trousers of heavy denim for manual work or casual wear
(used in the plural) close-fitting trousers of heavy denim for manual work or casual wear