poster vs placard

poster and placard both are nouns.

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

As nouns, poster and placard are synonyms defined as:

Other synonyms of poster include bill, card, notice, posting.

poster (noun)	placard (noun)
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
a sign posted in a public place as an advertisement
someone who pastes up bills or placards on walls or billboards

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