postman vs mail carrier

postman and mail carrier both are nouns.

Word	Noun	Adjective	Verb	Adverb
postman	Yes	No	No	No
mail carrier	Yes	No	No	No

As nouns, postman and mail carrier are synonyms defined as:

Other synonyms of postman include carrier, letter carrier, mailman.

postman (noun)	mail carrier (noun)
a man who delivers the mail	a man who delivers the mail