first blush vs notion

first blush and notion both are nouns.

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

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

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

first blush (noun)	notion (noun)
at the first glimpse or impression	(usually plural) small personal articles or clothing or sewing items
	a general inclusive concept
	an odd or fanciful or capricious idea
	a vague idea in which some confidence is placed