An idea or opinion formed beforehand, before having all the facts or evidence needed to make a fair judgment.
From Latin 'praeconcipere' (to conceive beforehand), combining 'prae-' (before) and 'concipere' (to conceive/form). Entered English in the 16th century in philosophical texts.
The phrase 'preconceived notion' is interesting because it assumes you can't actually avoid forming ideas—the real skill isn't having zero prior ideas but being aware you have them and testing them.
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