The Collaborative International Dictionary of English v.0.48:

Defiance \De*fi"ance\, n. [OF. defiance, desfiance, challenge,
   fr. desfier to challenge, F. d['e]fier. See Defy.]
   1. The act of defying, putting in opposition, or provoking to
      combat; a challenge; a provocation; a summons to combat.
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            A war without a just defiance made.   --Dryden.
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            Stood for her cause, and flung defiance down.
                                                  --Tennyson.
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   2. A state of opposition; willingness to flight; disposition
      to resist; contempt of opposition.
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            He breathed defiance to my ears.      --Shak.
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   3. A casting aside; renunciation; rejection. [Obs.] "Defiance
      to thy kindness." --Ford.
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   To bid defiance, To set at defiance, to defy; to
      disregard recklessly or contemptuously. --Locke.
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WordNet (r) 3.0 (2006):

defiance
    n 1: intentionally contemptuous behavior or attitude [syn:
         defiance, rebelliousness]
    2: a hostile challenge
    3: a defiant act