the condition of being insane; a derangement of the mind.

Law . such unsoundness of mind as affects legal responsibility or capacity.

Psychiatry . (formerly) psychosis.

extreme folly; senselessness; foolhardiness.

noun

balance , sanity , soundness , wellness , lucidity. , rationality

noun

aberration , absurdity , alienation , craziness , delirium , delusion , dementia , derangement , distraction , dotage , folly , frenzy , hallucination , hysteria , illusion , inanity , irrationality , irresponsibility , lunacy , madness , mania , mental disorder , neurosis , phobia , preposterousness , psychopathy , psychosis , senselessness , unbalance , unreasonableness , witlessness , brainsickness , disturbance , insaneness , mental illness , foolery , idiocy , imbecility , nonsense , silliness , tomfoolery , zaniness , aberrationof mind , alienation of mind , bedlamism , foolishness , monomania , paranoia