seafarer vs mariner

seafarer and mariner both are nouns.

Word	Noun	Adjective	Verb	Adverb
seafarer	Yes	No	No	No
mariner	Yes	No	No	No

As nouns, seafarer and mariner are synonyms defined as:

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

seafarer (noun)	mariner (noun)
a man who serves as a sailor	a man who serves as a sailor