Source : Webster's Revised Unabridged Dictionary (1913)

Brainsick \Brain"sick`\, a.
   Disordered in the understanding; giddy; thoughtless. --
   {Brain"sick*ness}, n.

Source : WordNet®

brainsick
     adj : affected with madness or insanity; "a man who had gone mad"
           [syn: {crazy}, {demented}, {distracted}, {disturbed}, {mad},
            {sick}, {unbalanced}, {unhinged}]