ship's officer vs mariner

ship's officer and mariner both are nouns.

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

As nouns, mariner is a hypernym of ship's officer; that is, mariner 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
mariner: a man who serves as a sailor

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

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