ship's officer vs seafarer

ship's officer and seafarer both are nouns.

Word	Noun	Adjective	Verb	Adverb
ship's officer	Yes	No	No	No
seafarer	Yes	No	No	No

As nouns, seafarer is a hypernym of ship's officer; that is, seafarer is a word with a broader meaning than ship's officer:

ship's officer: a person authorized to serve in a position of authority on a vessel
seafarer: a man who serves as a sailor

Other hypernyms of ship's officer include gob, Jack-tar, Jack, mariner, old salt, sea dog, seaman, tar.

ship's officer (noun)	seafarer (noun)
a person authorized to serve in a position of authority on a vessel	a man who serves as a sailor