poster vs flashcard

poster and flashcard both are nouns.

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

As nouns, flashcard is a hyponym of poster; that is, flashcard is a word with a more specific, narrower meaning than poster:

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

Other hyponyms of poster include show bill, show card, theatrical poster, flash card.

poster (noun)	flashcard (noun)
a horse kept at an inn or post house for use by mail carriers or for rent to travelers	a card with words or numbers or pictures that is flashed to a class by the teacher
a sign posted in a public place as an advertisement
someone who pastes up bills or placards on walls or billboards