mariner vs old salt

mariner and old salt both are nouns.

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

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

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

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