first blush vs opinion

first blush and opinion both are nouns.

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

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

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

first blush (noun)	opinion (noun)
at the first glimpse or impression	the reason for a court's judgment (as opposed to the decision itself)
	a personal belief or judgment that is not founded on proof or certainty
	a belief or sentiment shared by most people; the voice of the people
	a vague idea in which some confidence is placed
	the legal document stating the reasons for a judicial decision
	a message expressing a belief about something; the expression of a belief that is held with confidence but not substantiated by positive knowledge or proof