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1. Afflicted with or characteristic of mental derangement
   "was declared insane"; "insane laughter"
    
2. Very foolish
   "took insane risks behind the wheel";
   - harebrained, mad

Derived forms: insaner, insanest

See also: around the bend, balmy [archaic], barmy, bats, batty, bonkers, brainsick, buggy [N. Amer], certifiable, certified, crackbrained, cracked, crackers, crazed, crazy, cuckoo, daffy, daft, daft as a brush [Brit], demented, deranged, dippy, disturbed, dotty, dumb, fey, foolish, fruity, half-crazed, haywire, hebephrenic, idiotic, irrational, kookie, kooky, loco, loony, loopy, lunatic, mad, maniac, maniacal, manic-depressive, maniclike, mentally ill, moonstruck, non compos mentis, nuts, nutsy [N. Amer], nutty, of unsound mind, paranoid, potty [Brit], psychopathic, psychopathologic, psychopathological, psychotic, raving, raving mad, round the bend, round the twist [Brit], schizophrenic, screw-loose, screwy, sick, stupid, touched, unbalanced, unhinged, unreasonable, unsound, unstable, wacko, wacky, whacky, wild

Antonym: sane

Encyclopedia: Insane, Insane Again