insane

Concise Oxford English Dictionary © 2008 Oxford University Press:
insane/ɪnˈseɪn/

▶adjective

• 1 in or relating to an unsound state of mind; seriously mentally ill.

• 2 extremely foolish; irrational.

– derivatives
insanely adverb,
insanity noun (pl. insanities).

– origin C16: from L. insanus, from in- ‘not’ + sanus ‘healthy’.