Jack-tar vs old salt

Jack-tar and old salt both are nouns.

Word	Noun	Adjective	Verb	Adverb
Jack-tar	Yes	No	No	No
old salt	Yes	No	No	No

As nouns, Jack-tar and old salt are synonyms defined as:

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

Jack-tar (noun)	old salt (noun)
a man who serves as a sailor	a man who serves as a sailor