denim vs fabric

denim and fabric both are nouns.

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

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

denim: a coarse durable twill-weave cotton fabric
fabric: artifact made by weaving or felting or knitting or crocheting natural or synthetic fibers

Other hypernyms of denim include cloth, material, textile.

denim (noun)	fabric (noun)
a coarse durable twill-weave cotton fabric	artifact made by weaving or felting or knitting or crocheting natural or synthetic fibers
(used in the plural) close-fitting trousers of heavy denim for manual work or casual wear	the underlying structure