Source : Webster's Revised Unabridged Dictionary (1913)

Defy \De*fy"\, n.
   A challenge. [Obs.] --Dryden.

Defy \De*fy"\, v. t. [imp. & p. p. {Defied}; p. pr. & vb. n.
   {Defying}.] [F. d['e]fier, OF. deffier, desfier, LL.
   disfidare to disown faith or fidelity, to dissolve the bond
   of allegiance, as between the vassal and his lord; hence, to
   challenge, defy; fr. L. dis- + fides faith. See {Faith}, and
   cf. {Diffident}, {Affiance}.]
   1. To renounce or dissolve all bonds of affiance, faith, or
      obligation with; to reject, refuse, or renounce. [Obs.]

            I defy the surety and the bond.       --Chaucer.

            For thee I have defied my constant mistress. --Beau.
                                                  & Fl.

   2. To provoke to combat or strife; to call out to combat; to
      challenge; to dare; to brave; to set at defiance; to treat
      with contempt; as, to defy an enemy; to defy the power of
      a magistrate; to defy the arguments of an opponent; to
      defy public opinion.

            I once again Defy thee to the trial of mortal fight.
                                                  --Milton.

            I defy the enemies of our constitution to show the
            contrary.                             --Burke.

Source : WordNet®

defy
     v 1: resist or confront with resistance; "The politician defied
          public opinion"; "The new material withstands even the
          greatest wear and tear"; "The bridge held" [syn: {withstand},
           {hold}, {hold up}]
     2: elude, especially in a baffling way; "This behavior defies
        explanation" [syn: {resist}, {refuse}] [ant: {lend oneself}]
     3: challenge; "I dare you!" [syn: {dare}]
     [also: {defied}]