Source : Webster's Revised Unabridged Dictionary (1913)

Lunatic \Lu"na*tic\, n.
   A person affected by lunacy; an insane person, esp. one who
   has lucid intervals; a madman; a person of unsound mind.

         The lunatic, the lover, and the poet, Are of
         imagination all compact.                 --Shak.

Lunatic \Lu"na*tic\, a. [F. lunatique, L. lunaticus, fr. luna
   the moon. See {Lunar}.]
   1. Affected by lunacy; insane; mad.

            Lord, have mercy on my son; for he is lunatic.
                                                  --Wyclif
                                                  (Matt. xvii.
                                                  15).

   2. Of or pertaining to, or suitable for, an insane person;
      evincing lunacy; as, lunatic gibberish; a lunatic asylum.

Source : WordNet®

lunatic
     adj : insane and believed to be affected by the phases of the moon
           [syn: {moonstruck}]

lunatic
     n 1: an insane person [syn: {madman}, {maniac}]
     2: a reckless impetuous irresponsible person [syn: {daredevil},
         {madcap}, {hothead}, {swashbuckler}, {harum-scarum}]