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]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "blackout":
   KO, agnosia, amnesia, anoxia, asteroids, aurora particles,
   bamboo curtain, barrier of secrecy, blocking, brownout, catalepsy,
   catatonia, catatony, censorship, coma, cosmic particles,
   cosmic ray bombardment, curtain, dematerialization, departure,
   dimout, disappearance, disappearing, dispersion, dissipation,
   dissolution, dissolving, eclipse, elimination, erasure,
   evanescence, evaporation, extinction, fadeaway, fadeout, fading,
   faint, fugue, going, grayout, hush-up, intergalactic matter,
   iron curtain, ironbound security, kayo, knockout, lipothymia,
   lipothymy, loss of memory, melting, meteor dust impacts, meteors,
   nirvana, nirvana principle, nothingness, oath of secrecy, oblivion,
   obliviousness, occultation, official secrecy, pall, passing,
   pressure suit, radiation, repression, seal of secrecy, security,
   semiconsciousness, senselessness, sleep, smothering, space bullets,
   stifling, stupor, suppression, swoon, syncope, the bends,
   unconsciousness, vanishing, vanishing point, veil, veil of secrecy,
   weightlessness, wipe, word deafness, wraps