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]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "deactivate":
   break up, debrief, decommission, demilitarize, demob, demobilize,
   detach, disarm, disband, discharge, disintegrate, dismiss,
   disorganize, disperse, dissolve, go separate ways, let go,
   muster out, part, part company, reconvert, release, scatter,
   separate, sheathe the sword, split up