The Collaborative International Dictionary of English v.0.48:

Annihilate \An*ni"hi*late\, v. t. [imp. & p. p. Annihilated;
   p. pr. & vb. n. Annihilating.] [L. annihilare; ad +
   nihilum, nihil, nothing, ne hilum (filum) not a thread,
   nothing at all. Cf. File, a row.]
   1. To reduce to nothing or nonexistence; to destroy the
      existence of; to cause to cease to be.
      [1913 Webster]

            It impossible for any body to be utterly
            annihilated.                          --Bacon.
      [1913 Webster]

   2. To destroy the form or peculiar distinctive properties of,
      so that the specific thing no longer exists; as, to
      annihilate a forest by cutting down the trees. "To
      annihilate the army." --Macaulay.
      [1913 Webster]

   3. To destroy or eradicate, as a property or attribute of a
      thing; to make of no effect; to destroy the force, etc.,
      of; as, to annihilate an argument, law, rights, goodness.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

annihilating \annihilating\ adj.
   criticising vehemently and effectively; making light of; as,
   afire with annihilating invective.

   Syn: devastating, withering.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

annihilating
    adj 1: wreaking or capable of wreaking complete destruction;
           "possessing annihilative power"; "a devastating
           hurricane"; "the guns opened a withering fire" [syn:
           annihilative, annihilating, devastating,
           withering]
    2: making light of; "afire with annihilating invective"; "a
       devastating portrait of human folly"; "to compliments
       inflated I've a withering reply"- W.S.Gilbert [syn:
       annihilating, devastating, withering]