high brass vs brass

high brass and brass both are nouns.

Word	Noun	Adjective	Verb	Adverb
high brass	Yes	No	No	No
brass	Yes	No	No	No

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

high brass (noun)	brass (noun)
brass with 35% zinc	a wind instrument that consists of a brass tube (usually of variable length) that is blown by means of a cup-shaped or funnel-shaped mouthpiece
	a memorial made of brass
	an ornament or utensil made of brass
	impudent aggressiveness
	the persons (or committees or departments etc.) who make up a body for the purpose of administering something
	the section of a band or orchestra that plays brass instruments
	an alloy of copper and zinc