post horse vs post-horse

post horse and post-horse both are nouns.

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

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

post horse 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 post horse include poster.

post horse (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