The Collaborative International Dictionary of English v.0.48:

black out \black out\ v. i.
   to experience a temporary loss of consciousness, memory, or
   vision.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

black out \black out\ v. t.
   1. to cause to become black, such as a stage, a computer
      screen, or a city.
      [PJC]

   2. to impose a blackout on (news or a sports event).
      [PJC]

   3. to make (a written text) illegible by applying a black ink
      over it; to blot out.
      [PJC]

   4. to suppress (a memory).
      [PJC]

WordNet (r) 3.0 (2006):

black out
    v 1: obliterate or extinguish; "Some life-forms were obliterated
         by the radiation, others survived"
    2: darken completely; "The dining room blackened out" [syn:
       black out, blacken out]
    3: suppress by censorship as for political reasons; "parts of
       the newspaper article were blacked out"
    4: lose consciousness due to a sudden trauma, for example [syn:
       zonk out, pass out, black out]