sailor vs old salt

sailor and old salt both are nouns.

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

As nouns, old salt is a hyponym of sailor; that is, old salt is a word with a more specific, narrower meaning than sailor:

sailor (noun)	old salt (noun)
a stiff hat made of straw with a flat crown	a man who serves as a sailor
any member of a ship's crew
a serviceman in the navy