preconceived idea vs preconceived opinion

preconceived idea and preconceived opinion both are nouns.

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

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

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

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

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