top brass vs governance

top brass and governance both are nouns.

Word	Noun	Adjective	Verb	Adverb
top brass	Yes	No	No	No
governance	Yes	No	No	No

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

top brass: the most important persons in a governing body
governance: 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, governing body, organisation, organization.

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