placard vs flash card

placard and flash card both are nouns.

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

As nouns, flash card is a hyponym of placard; that is, flash card is a word with a more specific, narrower meaning than placard:

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

Other hyponyms of placard include show bill, show card, theatrical poster, flashcard.

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

placard (verb)	flash card (verb)
publicize or announce by placards
post in a public place