Source : Webster's Revised Unabridged Dictionary (1913)

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.

            Your kindred shuns your house As beaten hence by
            your strange lunacy.                  --Shak.

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

   Syn: Derangement; craziness; mania. See {Insanity}.

Source : WordNet®

lunacy
     n 1: obsolete terms for legal insanity [syn: {madness}, {insaneness}]
     2: foolish or senseless behavior [syn: {folly}, {foolery}, {tomfoolery},
         {craziness}, {indulgence}]