From Longman Dictionary of Contemporary Englishinsanein‧sane /ɪnˈseɪn/ ●○○ adjective 1 informalCRAZY completely stupid or crazy, often in a way that is dangerous That’s an insane risk. The whole idea sounds absolutely insane to me. Why did you do that? Have you gone insane?2 MIsomeone who is insane is permanently and seriously mentally ill so that they cannot live in normal society The killer was declared criminally insane.3 → the insane4 → drive somebody insane —insanely adverb insanely jealous She giggled insanely.
Examples from the Corpusinsane• Sometimes I thought I was going insane.• The man, who has attacked 13 women, was judged to be insane.• For some insane reason he decided to do the whole journey in one day.• Paul must be insane, spending all that money on a boat.• It would be insane to try to go camping in this kind of weather.