The Collaborative International Dictionary of English v.0.48:

existing \existing\ adj.
   1. having existence or being or actuality; as, much of the
      beluga caviar existing in the world is found in the Soviet
      Union and Iran. Opposite of nonexistent. [Narrower
      terms: active, alive; extant, surviving] Also See:
      extant.

   Syn: existent.
        [WordNet 1.5]

   2. Present. Opposite of absent.
      [WordNet 1.5]

   3. Presently existing; as, the existing system.
      [WordNet 1.5]