Source : Webster's Revised Unabridged Dictionary (1913)

Derangement \De*range"ment\, n. [Cf. F. d['e]rangement.]
   The act of deranging or putting out of order, or the state of
   being deranged; disarrangement; disorder; confusion;
   especially, mental disorder; insanity.

   Syn: Disorder; confusion; embarrassment; irregularity;
        disturbance; insanity; lunacy; madness; delirium; mania.
        See {Insanity}.

Source : WordNet®

derangement
     n 1: a state of mental disturbance and disorientation [syn: {mental
          unsoundness}, {unbalance}]
     2: the act of disturbing the mind or body; "his carelessness
        could have caused an ecological upset"; "she was
        unprepared for this sudden overthrow of their normal way
        of living" [syn: {upset}, {overthrow}]