Source : Webster's Revised Unabridged Dictionary (1913)

Insane \In*sane"\, a. [L. insanus. See {In-} not, and {Sane}.]
   1. Exhibiting unsoundness or disorded of mind; not sane; mad;
      deranged in mind; delirious; distracted. See {Insanity},
      2.

   2. Used by, or appropriated to, insane persons; as, an insane
      hospital.

   3. Causing insanity or madness. [R.]

            Or have we eaten on the insaneroot That takes the
            reason prisoner ?                     --Shak.

   4. Characterized by insanity or the utmost folly; chimerical;
      unpractical; as, an insane plan, attempt, etc.

            I know not which was the insane measure. --Southey.

Source : WordNet®

insane
     adj 1: afflicted with or characteristic of mental derangement; "was
            declared insane"; "insane laughter" [ant: {sane}]
     2: very foolish; "harebrained ideas"; "took insane risks behind
        the wheel"; "a completely mad scheme to build a bridge
        between two mountains" [syn: {harebrained}, {mad}]