| 1. | insanity; mental disorder. |
| 2. | intermittent insanity, formerly believed to be related to phases of the moon. |
| 3. | extreme foolishness or an instance of it: Her decision to resign was sheer lunacy. |
| 4. | Law. unsoundness of mind sufficient to incapacitate one for civil transactions. |
lu·na·cy (lōō'nə-sē) n. pl. lu·na·cies
[From lunatic.] |