/looh"neuh see/ , n. , pl. lunacies .
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.
[ 1535-45; LUN(ATIC) + -ACY ]
Syn. 1. derangement, dementia; craziness, madness, mania, aberration. 3. folly, stupidity.
Ant. 1, 2. rationality, sanity.