/ ɪnˈseɪn; NAmE / adjective
1.
seriously mentally ill and unable to live in normal society :
Doctors certified him as insane.
The prisoners were slowly going insane .
OPP sane ➡ note at mentally ill
2.
the insane noun [ pl. ] people who are insane :
a hospital for the insane
3.
( informal ) very stupid, crazy or dangerous :
I must have been insane to agree to the idea.
This job is driving me insane (= making me feel very angry) .
—see also insanity
► in·sane·ly adverb :
He is insanely jealous.
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WORD ORIGIN
mid 16th cent.: from Latin insanus , from in- not + sanus healthy.