Source : Webster's Revised Unabridged Dictionary (1913)

Disannul \Dis`an*nul"\, v. t.
   To annul completely; to render void or of no effect.

         For the Lord of hosts hath purposed, and who shall
         disannul it?                             --Isaiah xiv.
                                                  27.

   Note: The prefix in this word an its derivatives is
         intensive, and not negative.