From Longman Dictionary of Contemporary Englishinsanityin‧san‧i‧ty /ɪnˈsænəti/ noun [uncountable] 1 SCLMIthe state of being seriously mentally ill, so that you cannot live normally in society SYN madness The court acquitted Campbell on the grounds of temporary insanity.2 STUPID/NOT INTELLIGENTvery stupid actions that may cause you serious harm SYN lunacy Can’t they see the insanity of dumping radioactive waste in the sea?
Examples from the Corpus
insanity• Hodge was found not guilty by reason of insanity.• Hearing voices inside your head is a common symptom of insanity.• It was sheer insanity to try to drive through the mountains in that thunderstorm.• Brennan blames her actions on temporary insanity. 