The Collaborative International Dictionary of English v.0.48:

Annihilation \An*ni`hi*la"tion\, n. [Cf. F. annihilation.]
   1. The act of reducing to nothing, or nonexistence; or the
      act of destroying the form or combination of parts under
      which a thing exists, so that the name can no longer be
      applied to it; as, the annihilation of a corporation.
      [1913 Webster]

   2. The state of being annihilated. --Hooker.
      [1913 Webster]

WordNet (r) 3.0 (2006):

annihilation
    n 1: destruction by annihilating something [syn: annihilation,
         obliteration]
    2: total destruction; "bomb tests resulted in the annihilation
       of the atoll" [syn: annihilation, disintegration]