drivel vs subject matter

drivel and subject matter both are nouns.

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

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

Other hypernyms of drivel include content, message, substance.

drivel (noun)	subject matter (noun)
saliva spilling from the mouth	content communicating a message; what something is about
a worthless message

drivel (verb)	subject matter (verb)
let saliva drivel from the mouth