Meaning of INSANITY in English

INSANITY

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?

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.