The Collaborative International Dictionary of English v.0.48:

Lunacy \Lu"na*cy\, n.; pl. Lunacies. [See Lunatic.]
   1. Insanity or madness; properly, the kind of insanity which
      is broken by intervals of reason, -- formerly supposed to
      be influenced by the changes of the moon; any form of
      unsoundness of mind, except idiocy; mental derangement or
      alienation. --Brande. --Burrill.
      [1913 Webster]

            Your kindred shuns your house
            As beaten hence by your strange lunacy. --Shak.
      [1913 Webster]

   2. A morbid suspension of good sense or judgment, as through
      fanaticism. --Dr. H. More.

   Syn: Derangement; craziness; mania. See Insanity.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "lunacy":
   aberration, abnormality, absurdity, alienation, asininity,
   battiness, brain damage, brainlessness, brainsickness, buffoonery,
   clouded mind, clownishness, crackpottedness, crankiness, craziness,
   daffiness, daftness, dementedness, dementia, derangement,
   desipience, disorientation, distraction, eccentricity, fatuity,
   fatuousness, folie, folly, foolery, foolhardiness, foolheadedness,
   foolishness, frivolity, frivolousness, furor, giddiness, goofiness,
   idiocy, illogic, illogicality, imbecility, inanity, ineptitude,
   insaneness, insanity, irrationality, loss of mind, loss of reason,
   madness, mania, mental deficiency, mental derangement,
   mental disease, mental disorder, mental disturbance,
   mental illness, mental instability, mental sickness,
   mind overthrown, mindlessness, mindsickness, niaiserie, nugacity,
   nuttiness, oddness, pixilation, possession, preposterousness,
   psychopathy, psychosis, queerness, rabidness, reasonlessness,
   ridiculousness, sappiness, screwiness, senselessness,
   shattered mind, sick mind, sickness, silliness, strangeness,
   stupidity, thoughtlessness, triflingness, triviality, unbalance,
   unbalanced mind, unsaneness, unsound mind, unsoundness,
   unsoundness of mind, wackiness, weirdness, witlessness, zaniness,
   zanyism