in ‧ san ‧ i ‧ ty /ɪnˈsænəti, ɪnˈsænɪti/ BrE AmE noun [uncountable]
1 . the 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 . very stupid actions that may cause you serious harm SYN lunacy :
Can’t they see the insanity of dumping radioactive waste in the sea?