top brass vs governing body

top brass and governing body both are nouns.

Word	Noun	Adjective	Verb	Adverb
top brass	Yes	No	No	No
governing body	Yes	No	No	No

As nouns, governing body is a hypernym of top brass; that is, governing body is a word with a broader meaning than top brass:

top brass: the most important persons in a governing body
governing body: the persons (or committees or departments etc.) who make up a body for the purpose of administering something

Other hypernyms of top brass include administration, brass, establishment, governance, organisation, organization.

top brass (noun)	governing body (noun)
the most important persons in a governing body	the persons (or committees or departments etc.) who make up a body for the purpose of administering something