workwear vs denim

workwear and denim both are nouns.

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

As nouns, denim is a hyponym of workwear; that is, denim is a word with a more specific, narrower meaning than workwear:

workwear: heavy-duty clothes for manual or physical work
denim: (used in the plural) close-fitting trousers of heavy denim for manual work or casual wear

Other hyponyms of workwear include blue jeans, jeans, work-shirt.

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