denim vs workwear

denim and workwear both are nouns.

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

As nouns, workwear is a hypernym of denim; that is, workwear 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
workwear: heavy-duty clothes for manual or physical work

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

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