approval vs subject matter

approval and subject matter both are nouns.

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

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

Other hypernyms of approval include content, message, substance.

approval (noun)	subject matter (noun)
the formal act of approving	content communicating a message; what something is about
a message expressing a favorable opinion
a feeling of liking something or someone good
acceptance as satisfactory