subject matter vs communication

subject matter and communication both are nouns.

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

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

subject matter: content communicating a message; what something is about
communication: something that is communicated by or to or between people or groups

subject matter (noun)	communication (noun)
content communicating a message; what something is about	something that is communicated by or to or between people or groups
	the activity of communicating; the activity of conveying information
	a connection allowing access between persons or places