first blush vs belief

first blush and belief both are nouns.

Word	Noun	Adjective	Verb	Adverb
first blush	Yes	No	No	No
belief	Yes	No	No	No

As nouns, belief is a hypernym of first blush; that is, belief is a word with a broader meaning than first blush:

Other hypernyms of first blush include feeling, impression, notion, opinion.

first blush (noun)	belief (noun)
at the first glimpse or impression	any cognitive content held as true
	a vague idea in which some confidence is placed