The Collaborative International Dictionary of English v.0.48:

Neutralize \Neu"tral*ize\, v. t. [imp. & p. p. Neutralized; p.
   pr. & vb. n. Neutralizing.] [Cf. F. neutraliser.]
   1. To render neutral; to reduce to a state of neutrality.
      [1913 Webster]

            So here I am neutralized again.       --Sir W.
                                                  Scott.
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   2. (Chem.) To render inert or imperceptible the peculiar
      affinities of, as a chemical substance; to destroy the
      effect of; as, to neutralize an acid with a base.
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   3. To destroy the peculiar properties or opposite
      dispositions of; to reduce to a state of indifference or
      inefficiency; to counteract; to render ineffective; as, to
      neutralize parties in government; to neutralize efforts,
      opposition, etc.
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            Counter citations that neutralize each other. --E.
                                                  Everett.
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WordNet (r) 3.0 (2006):

neutralize
    v 1: make politically neutral and thus inoffensive; "The treaty
         neutralized the small republic"
    2: make ineffective by counterbalancing the effect of; "Her
       optimism neutralizes his gloom"; "This action will negate the
       effect of my efforts" [syn: neutralize, neutralise,
       nullify, negate]
    3: oppose and mitigate the effects of by contrary actions; "This
       will counteract the foolish actions of my colleagues" [syn:
       counteract, countervail, neutralize, counterbalance]
    4: get rid of (someone who may be a threat) by killing; "The
       mafia liquidated the informer"; "the double agent was
       neutralized" [syn: neutralize, neutralise, liquidate,
       waste, knock off, do in]
    5: make incapable of military action [syn: neutralize,
       neutralise]
    6: make chemically neutral; "She neutralized the solution" [syn:
       neutralize, neutralise]