mariner vs seafarer

mariner and seafarer both are nouns.

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

As nouns, mariner and seafarer are synonyms defined as:

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

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