letter carrier vs postman

letter carrier and postman both are nouns.

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

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

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

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