top brass vs establishment

top brass and establishment both are nouns.

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

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

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

top brass (noun)	establishment (noun)
the most important persons in a governing body	the act of forming or establishing something
	a public or private structure (business or governmental or educational) including buildings and equipment for business or residence
	the cognitive process of establishing a valid proof
	an organization founded and united for a specific purpose
	any large organization
	the persons (or committees or departments etc.) who make up a body for the purpose of administering something
	(ecology) the process by which a plant or animal becomes established in a new habitat