denim vs trousers

denim and trousers both are nouns.

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

As nouns, trousers is a hypernym of denim; that is, trousers is a word with a broader meaning than denim:

denim: (used in the plural) close-fitting trousers of heavy denim for manual work or casual wear
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

Other hypernyms of denim include pair of trousers, pant, workwear.

denim (noun)	trousers (noun)
a coarse durable twill-weave cotton fabric	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately
(used in the plural) close-fitting trousers of heavy denim for manual work or casual wear