preconceived opinion vs preconceived notion

preconceived opinion and preconceived notion both are nouns.

Word	Noun	Adjective	Verb	Adverb
preconceived opinion	Yes	No	No	No
preconceived notion	Yes	No	No	No

As nouns, preconceived opinion and preconceived notion are synonyms defined as:

preconceived opinion and preconceived notion: an opinion formed beforehand without adequate evidence

Other synonyms of preconceived opinion include parti pris, preconceived idea, preconception, prepossession.

preconceived opinion (noun)	preconceived notion (noun)
an opinion formed beforehand without adequate evidence	an opinion formed beforehand without adequate evidence