bo'sun vs sea dog

bo'sun and sea dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
bo'sun	Yes	No	No	No
sea dog	Yes	No	No	No

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

bo'sun: 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 bo'sun include gob, Jack-tar, Jack, mariner, old salt, seafarer, seaman, tar.

bo'sun (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