An idiot, dolt, or dullard is a mentally deficient person, or someone who acts in a self-defeating or significantly counterproductive way. Archaically the word mome has also been used. The synonymous terms moron, imbecile, and cretin have all gained specialized meanings in modern times. An idiot is said to be idiotic, and to suffer from idiocy. A dunce is an idiot who is specifically incapable of learning. An idiot differs from a fool (who is unwise) and an ignoramus (who is uneducated/an ignorant), neither of which refer to someone with low intelligence.
"Idiot" originally referred to "layman, person lacking professional skill", "person so mentally deficient as to be incapable of ordinary reasoning". Declining to take part in public life, such as democratic government of the polis (city state), such as the Athenian democracy, was considered dishonorable. "Idiots" were seen as having bad judgment in public and political matters. Over time, the term "idiot" shifted away from its original connotation of selfishness and came to refer to individuals with overall bad judgment–individuals who are "stupid". In modern English usage, the terms "idiot" and "idiocy" describe an extreme folly or stupidity, and its symptoms (foolish or stupid utterance or deed). In psychology, it is a historical term for the state or condition now called profound mental retardation.
Idiot as a word derived from the Greek, idio-te-s ("person lacking professional skill," "a private citizen," "individual"), from idios ("private," "one's own"). In Latin the word idiota ("ordinary person, layman") preceded the Late Latin meaning "uneducated or ignorant person." Its modern meaning and form dates back to Middle English around the year 1300, from the Old French idiote ("uneducated or ignorant person"). The related word idiocy dates to 1487 and may have been analogously modeled on the words prophet and prophecy. The word has cognates in many other languages.