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: Webster's Revised Unabridged Dictionary (1913)