preconceived opinion vs preconceived idea

preconceived opinion and preconceived idea both are nouns.

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

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

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

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

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