bargeman vs sea dog

bargeman and sea dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
bargeman	Yes	No	No	No
sea dog	Yes	No	No	No

As nouns, sea dog is a hypernym of bargeman; that is, sea dog is a word with a broader meaning than bargeman:

Other hypernyms of bargeman include gob, Jack-tar, Jack, mariner, old salt, seafarer, seaman, tar.

bargeman (noun)	sea dog (noun)
someone who operates a barge	a man who serves as a sailor