The Collaborative International Dictionary of English v.0.48:

deactivate \de*ac"ti*vate\, v. t.
   1. To make inactive; to render ineffective; as, to deactivate
      a bomb; to deactivate a machine; to deactivate the alarm.

   Note: The deactivation of a machine or device is usually a
         reversible process; switching off an electrical device
         may be referred to as deactivation. To render an enzyme
         or catalyst ineffective is more commonly referred to as
         to inactivate.
         [PJC]

   2. To disband (a military unit, or other group); to
      discontinue (a group activity); as, to deactivate the
      regiment; to deactivate the investigation.
      [PJC]

WordNet (r) 3.0 (2006):

deactivate
    v 1: remove from active military status or reassign; "The men
         were deactivated after five years of service"
    2: make inactive; "they deactivated the file" [syn:
       inactivate, deactivate] [ant: activate]