top billing vs advertisement

top billing and advertisement both are nouns.

Word	Noun	Adjective	Verb	Adverb
top billing	Yes	No	No	No
advertisement	Yes	No	No	No

As nouns, advertisement is a hypernym of top billing; that is, advertisement is a word with a broader meaning than top billing:

top billing: the advertisement of a star's name at the top of a theatrical poster
advertisement: a public promotion of some product or service

Other hypernyms of top billing include ad, advert, advertising, advertizement, advertizing.

top billing (noun)	advertisement (noun)
the advertisement of a star's name at the top of a theatrical poster	a public promotion of some product or service