nonsense vs subject matter

nonsense and subject matter both are nouns.

Word	Noun	Adjective	Verb	Adverb
nonsense	Yes	Yes	No	No
subject matter	Yes	No	No	No

As nouns, subject matter is a hypernym of nonsense; that is, subject matter is a word with a broader meaning than nonsense:

Other hypernyms of nonsense include content, message, substance.

nonsense (noun)	subject matter (noun)
ornamental objects of no great value	content communicating a message; what something is about
a message that seems to convey no meaning

nonsense (adjective)	subject matter (adjective)
having no intelligible meaning