The Collaborative International Dictionary of English v.0.48:

Derange \De*range"\, v. t. [imp. & p. p. Deranged; p. pr. &
   vb. n. Deranging.] [F. d['e]ranger; pref. d['e]- = d['e]s-
   (L. dis) + ranger to range. See Range, and cf.
   Disarrange, Disrank.]
   1. To put out of place, order, or rank; to disturb the proper
      arrangement or order of; to throw into disorder,
      confusion, or embarrassment; to disorder; to disarrange;
      as, to derange the plans of a commander, or the affairs of
      a nation.
      [1913 Webster]

   2. To disturb in action or function, as a part or organ, or
      the whole of a machine or organism.
      [1913 Webster]

            A sudden fall deranges some of our internal parts.
                                                  --Blair.
      [1913 Webster]

   3. To disturb in the orderly or normal action of the
      intellect; to render insane.

   Syn: To disorder; disarrange; displace; unsettle; disturb;
        confuse; discompose; ruffle; disconcert.
        [1913 Webster]

WordNet (r) 3.0 (2006):

derange
    v 1: derange mentally, throw out of mental balance; make insane;
         "The death of his parents unbalanced him" [syn:
         unbalance, derange]
    2: throw into great confusion or disorder; "Fundamental
       Islamicists threaten to perturb the social order in Algeria
       and Egypt" [syn: perturb, derange, throw out of kilter]