Insanity \In*san"i*ty\, n. [L. insanitas unsoundness; cf. insania insanity, F. insanite.]

1. The state of being insane; unsoundness or derangement of mind; madness; lunacy.

All power of fancy overreason is a degree of insanity. --Johnson.

Without grace The heart's insanity admits no cure. --Cowper.

2. (Law) Such a mental condition, as, either from the existence of delusions, or from incapacity to distinguish between right and wrong, with regard to any matter under action, does away with individual responsibility.

Syn: Syn>- Insanity, Lunacy, Madness, Derangement, Aliention, Aberration, Mania, Delirium, Frenzy, Monomania, Dementia.

Usage: Insanity is the generic term for all such diseases; lunacy has now an equal extent of meaning, though once used to denote periodical insanity; madness has the same extent, though originally referring to the rage created by the disease; derangement, alienation, are popular terms for insanity; delirium, mania, and frenzy denote excited states of the disease; dementia denotes the loss of mental power by this means; monomania is insanity upon a single subject.

Source: Webster's Revised Unabridged Dictionary (1913)