brass hat vs military officer

brass hat and military officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
brass hat	Yes	No	No	No
military officer	Yes	No	No	No

As nouns, military officer is a hypernym of brass hat; that is, military officer is a word with a broader meaning than brass hat:

brass hat: a high-ranking military officer
military officer: any person in the armed services who holds a position of authority or command

Other hypernyms of brass hat include officer.

brass hat (noun)	military officer (noun)
a high-ranking military officer	any person in the armed services who holds a position of authority or command