/ ɪnˈsænəti; NAmE / noun [ U ]
1.
the state of being insane
SYN madness :
He was found not guilty, by reason of insanity.
OPP sanity
2.
actions that are very stupid and possibly dangerous
SYN madness , lunacy :
It would be sheer insanity to attempt the trip in such bad weather.
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WORD ORIGIN
late 16th cent.: from Latin insanitas , from insanus , from in- not + sanus healthy.