The Collaborative International Dictionary of English v.0.48:

Lunatic \Lu"na*tic\, a. [F. lunatique, L. lunaticus, fr. luna
   the moon. See Lunar.]
   1. Affected by lunacy; insane; mad; crazy; demented.
      [1913 Webster]

            Lord, have mercy on my son; for he is lunatic.
                                                  --Wyclif
                                                  (Matt. xvii.
                                                  15).
      [1913 Webster]

   2. Of or pertaining to, or suitable for, an insane person;
      evincing lunacy; as, lunatic gibberish; a lunatic asylum.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         The lunatic, the lover, and the poet,
         Are of imagination all compact.          --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lunatic
    adj 1: insane and believed to be affected by the phases of the
           moon [syn: lunatic, moonstruck]
    n 1: an insane person [syn: lunatic, madman, maniac]
    2: a reckless impetuous irresponsible person [syn: daredevil,
       madcap, hothead, swashbuckler, lunatic, harum-
       scarum]

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "lunatic":
   abnormal, absurd, aliene, ass, balmy, batty, bedlamite,
   bereft of reason, borderline case, born fool, brainsick, buffoon,
   clown, crackbrain, crackbrained, cracked, crackpot, crank, crazed,
   crazy, cuckoo, daft, deluded, dement, demented, demoniac,
   deprived of reason, deranged, ding-a-ling, disoriented, distraught,
   doodle, egregious ass, energumen, fanatic, fantastic,
   figure of fun, flake, flighty, fool, fou, hallucinated, harebrain,
   idiot, ignoramus, insane, irrational, jackass, kook, loco, loon,
   loony, mad, maddened, madman, maniac, manic, mazed, mental,
   mentally deficient, meshuggah, meshuggenah, milksop, moon-struck,
   mooncalf, neuropath, neurotic, non compos, non compos mentis,
   noncompos, not all there, not right, nut, odd, of unsound mind,
   off, paranoid, perfect fool, phrenetic, potty, preposterous,
   psycho, psychoneurotic, queer, raver, raving lunatic, reasonless,
   schmuck, screwball, senseless, sick, softhead, sop, stark-mad,
   stark-staring mad, strange, stupid ass, tetched, tomfool, touched,
   unbalanced, unhinged, unsane, unsettled, unsound, wacky, wandering,
   weirdo, witless, zany



Easton's 1897 Bible Dictionary:

Lunatic
   probably the same as epileptic, the symptoms of which disease
   were supposed to be more aggravated as the moon increased. In
   Matt. 4:24 "lunatics" are distinguished from demoniacs. In 17:15
   the name "lunatic" is applied to one who is declared to have
   been possessed. (See DAEMONIAC.)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

LUNATIC, persons. One who has had an understanding, but who, by disease,
grief, or other accident, has lost the use of his reason. A lunatic is
properly one who has had lucid intervals, sometimes enjoying his senses, and
sometimes not. 4 Co. 123; 1 Bl. Com. 304; Bac. Abr. Idiots, &c., A; 1 Russ.
on Crimes, 8; Shelf. on Lun. 4; Merlin, mot Demence; Fonb. Eq. Index, h.t.;
15 Vin. Ab. 131; 8 Com. Dig. 721; 1 Supp. to Ves. jr. 94, 130, 369, 404;
2 Supp. to Ves. jr. 51, 106, 151, 360; 1 Vern. 9, 137, 262; Louis. Code,
tit. 9, c. 1; and articles Lucid Interval; Lunacy.