bosun vs sea dog

bosun and sea dog both are nouns.

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

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

bosun: a petty officer on a merchant ship who controls the work of other seamen
sea dog: a man who serves as a sailor

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

bosun (noun)	sea dog (noun)
a petty officer on a merchant ship who controls the work of other seamen	a man who serves as a sailor