blue blood vs brahman

blue blood and brahman both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue blood	Yes	No	No	No
brahman	Yes	No	No	No

As nouns, brahman is a hyponym of blue blood; that is, brahman is a word with a more specific, narrower meaning than blue blood:

blue blood: a member of the aristocracy
brahman: a member of a social and cultural elite (especially a descendant of an old New England family)

blue blood (noun)	brahman (noun)
a member of the aristocracy	the highest of the four varnas: the priestly or sacerdotal category
	a member of the highest of the four Hindu varnas
	a member of a social and cultural elite (especially a descendant of an old New England family)