opinion vs first blush

opinion and first blush both are nouns.

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

As nouns, first blush is a hyponym of opinion; that is, first blush is a word with a more specific, narrower meaning than opinion:

Other hyponyms of opinion include presence, effect, hunch, intuition, suspicion.

opinion (noun)	first blush (noun)
the reason for a court's judgment (as opposed to the decision itself)	at the first glimpse or impression
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