The Collaborative International Dictionary of English v.0.48:

blackout \blackout\ n.
   1. a suspension of radio or tv broadcasting.
      [WordNet 1.5]

   2. any darkness resulting from the extinction of lights.
      [WordNet 1.5]

   3. the failure of electric power for a general region
      sufficient to extinguish all normal lighting.

   Syn: brownout, dimout.
        [WordNet 1.5]

   4. a momentary loss of consciousness.
      [WordNet 1.5]

   5. partial or total loss of memory. he has a total blackout
      for events of the evening

   Syn: amnesia, memory loss.
        [WordNet 1.5]

   6. a period during which artificial lighting is forbidden, as
      in a city as a precaution against an air raid.
      [PJC]

   7. (Theater) the darkening of all stage lights, as at then
      end of a performance or between acts.
      [PJC]

   8. suppression of information distribution; as, there was a
      blackout on news from the military for the first day of
      the Gulf War.
      [PJC]

   9. the prohibition of the broadcasting of a sports event,
      such as a boxing match or football game, sometimes
      confined to one particular area. It is usually done to
      encourage sales of tickets to the event.
      [PJC]

WordNet (r) 3.0 (2006):

blackout
    n 1: a suspension of radio or tv broadcasting
    2: darkness resulting from the extinction of lights (as in a
       city invisible to enemy aircraft) [syn: blackout,
       brownout, dimout]
    3: the failure of electric power for a general region
    4: a momentary loss of consciousness
    5: partial or total loss of memory; "he has a total blackout for
       events of the evening" [syn: amnesia, memory loss,
       blackout]