The Etymology of Idiot
Idiot has travelled a long way from the Athenian agora. The Greek noun idiṓtēs (ἰδιώτης) was built from the adjective idios (one's own, private) and named a private citizen — someone whose life was bounded by household and personal affairs rather than public office. In democratic Athens the word was descriptive, not contemptuous, but already had a faint edge: an idiōtēs who refused public service was failing in civic duty, and an idiōtēs in any specialist field was simply a layperson, an outsider to the technical knowledge of doctors, soldiers, or sailors. By Hellenistic and Roman times this had hardened into the meaning ignorant person, and Latin idiōta carried that pejorative sense. English borrowed the word in the late 14th century already in the unflattering meaning, and it has stayed there. Nineteenth-century medicine briefly used idiot as a clinical term for severe intellectual disability, a usage now obsolete and considered offensive. The Greek root idios survives more neutrally in idiom (one's own way of speaking), idiosyncrasy, and idiopathic.