Source : Webster's Revised Unabridged Dictionary (1913)

Idiot \Id"i*ot\, n. [F. idiot, L. idiota an uneducated,
   ignorant, ill-informed person, Gr. ?, also and orig., a
   private person, not holding public office, fr. ? proper,
   peculiar. See {Idiom}.]
   1. A man in private station, as distinguished from one
      holding a public office. [Obs.]

            St. Austin affirmed that the plain places of
            Scripture are sufficient to all laics, and all
            idiots or private persons.            --Jer. Taylor.

   2. An unlearned, ignorant, or simple person, as distinguished
      from the educated; an ignoramus. [Obs.]

            Christ was received of idiots, of the vulgar people,
            and of the simpler sort, while he was rejected,
            despised, and persecuted even to death by the high
            priests, lawyers, scribes, doctors, and rabbis. --C.
                                                  Blount.

   3. A human being destitute of the ordinary intellectual
      powers, whether congenital, developmental, or accidental;
      commonly, a person without understanding from birth; a
      natural fool; a natural; an innocent.

            Life . . . is a tale Told by an idiot, full of sound
            and fury, Signifying nothing.         --Shak.

   4. A fool; a simpleton; -- a term of reproach.

            Weenest thou make an idiot of our dame? --Chaucer.

Source : WordNet®

idiot
     n : a person of subnormal intelligence [syn: {imbecile}, {cretin},
          {moron}, {changeling}, {half-wit}, {retard}]