ad vs promo

ad and promo both are nouns.

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

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

ad: a public promotion of some product or service
promo: a message issued in behalf of some product or cause or idea or person or institution

Other hypernyms of ad include packaging, promotion, promotional material, publicity.

ad (noun)	promo (noun)
a public promotion of some product or service	a message issued in behalf of some product or cause or idea or person or institution