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

Derived forms: insaner, insanest

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

Antonym: sane

Encyclopedia: Insane, Insane Again