flash card vs poster

flash card and poster both are nouns.

Word	Noun	Adjective	Verb	Adverb
flash card	Yes	No	No	No
poster	Yes	No	No	No

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

flash card: a card with words or numbers or pictures that is flashed to a class by the teacher
poster: a sign posted in a public place as an advertisement

Other hypernyms of flash card include bill, card, notice, placard, posting.

flash card (noun)	poster (noun)
a card with words or numbers or pictures that is flashed to a class by the teacher	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