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 over reason 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. -- Insanity, Lunacy, Madness,
Derangement, Alienation, Aberration,
Mania, Delirium, Frenzy, Monomania,
Dementia. 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.