promo vs message

promo and message both are nouns.

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

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

promo: a message issued in behalf of some product or cause or idea or person or institution
message: content communicating a message; what something is about

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

promo (noun)	message (noun)
a message issued in behalf of some product or cause or idea or person or institution	content communicating a message; what something is about
	a communication (usually brief) that is written or spoken or signaled