ad vs publicity

ad and publicity both are nouns.

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

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

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

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

ad (noun)	publicity (noun)
a public promotion of some product or service	the quality of being open to public view
	a message issued in behalf of some product or cause or idea or person or institution