brahman vs blue blood

brahman and blue blood both are nouns.

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

As nouns, blue blood is a hypernym of brahman; that is, blue blood is a word with a broader meaning than brahman:

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

Other hypernyms of brahman include aristocrat, patrician.

brahman (noun)	blue blood (noun)
the highest of the four varnas: the priestly or sacerdotal category	a member of the aristocracy
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)