seafarer vs old salt

seafarer and old salt both are nouns.

Word	Noun	Adjective	Verb	Adverb
seafarer	Yes	No	No	No
old salt	Yes	No	No	No

As nouns, seafarer and old salt are synonyms defined as:

Other synonyms of seafarer include gob, Jack-tar, Jack, mariner, sea dog, seaman, tar.

seafarer (noun)	old salt (noun)
a man who serves as a sailor	a man who serves as a sailor