sea dog vs mariner

sea dog and mariner both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea dog	Yes	No	No	No
mariner	Yes	No	No	No

As nouns, sea dog and mariner are synonyms defined as:

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

sea dog (noun)	mariner (noun)
a man who serves as a sailor	a man who serves as a sailor