Jack vs seafarer

Jack and seafarer both are nouns.

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

As nouns, Jack and seafarer are synonyms defined as:

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

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