poster vs post horse

poster and post horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
poster	Yes	No	No	No
post horse	Yes	No	No	No

As nouns, poster and post horse are synonyms defined as:

poster and post horse: a horse kept at an inn or post house for use by mail carriers or for rent to travelers

Other synonyms of poster include post-horse.

poster (noun)	post horse (noun)
a horse kept at an inn or post house for use by mail carriers or for rent to travelers	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