top brass vs administration

top brass and administration both are nouns.

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

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

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

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

top brass (noun)	administration (noun)
the most important persons in a governing body	a method of tending to or managing the affairs of some group of people (especially the group's business affairs)
	the act of administering medication
	the act of meting out justice according to the law
	the act of governing; exercising authority
	the persons (or committees or departments etc.) who make up a body for the purpose of administering something
	the tenure of a president