theatrical poster vs poster

theatrical poster and poster both are nouns.

Word	Noun	Adjective	Verb	Adverb
theatrical poster	Yes	No	No	No
poster	Yes	No	No	No

As nouns, poster is a hypernym of theatrical poster; that is, poster is a word with a broader meaning than theatrical poster:

Other hypernyms of theatrical poster include bill, card, notice, placard, posting.

theatrical poster (noun)	poster (noun)
a poster advertising a show or play	a horse kept at an inn or post house for use by mail carriers or for rent to travelers
	a sign posted in a public place as an advertisement
	someone who pastes up bills or placards on walls or billboards