helmsman vs mariner

helmsman and mariner both are nouns.

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

As nouns, mariner is a hypernym of helmsman; that is, mariner is a word with a broader meaning than helmsman:

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

helmsman (noun)	mariner (noun)
the person who steers a ship	a man who serves as a sailor