proposal vs message

proposal and message both are nouns.

Word	Noun	Adjective	Verb	Adverb
proposal	Yes	No	No	No
message	Yes	No	Yes	No

As nouns, message is a hypernym of proposal; that is, message is a word with a broader meaning than proposal:

Other hypernyms of proposal include content, subject matter, substance.

proposal (noun)	message (noun)
something proposed (such as a plan or assumption)	content communicating a message; what something is about
the act of making a proposal	a communication (usually brief) that is written or spoken or signaled
an offer of marriage