en.wiktionary.org/wiki/idiot

"From Middle English from Old French idiote from Latin idiota from Ancient Greek ἰδιώτης (idiotēs), “‘a private citizen, one who has no professional knowledge, layman’”) from ἴδιος (idios), “‘one's own, pertaining to oneself, private’”); ἰδιώτης was used derisively in ancient Athens to refer to one who declined to take part in public life."