idiot

n. fool, dunce, simpleton; person who is severely mentally handicapped

Idiot is a word derived from the Greek , idiōtēs ("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.
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Idiot /id·i·ot/ obsolete, offensive name for a person with profound mental retardation. idiot savant a mentally retarded person with a particular [more]Idiot - Community and Resources

Noun
1. a person of subnormal intelligence
(synonym) imbecile, cretin, moron, changeling, half-wit, retard
(hypernym) simpleton, simple

n. idiot, fool, dunce, asshole, jackass, stupid person