Source : Webster's Revised Unabridged Dictionary (1913)

Undoing \Un*do"ing\, n.
   1. The reversal of what has been done.

   2. Ruin. ``The utter undoing of some.'' --Hooker.

Source : WordNet®

undoing
     n 1: an act that makes a previous act of no effect (as if not
          done)
     2: loosening the ties that fasten something; "the tying of bow
        ties is an art; the untying is easy" [syn: {untying}, {unfastening}]