The Collaborative International Dictionary of English v.0.48:

Voidance \Void"ance\, n.
   1. The act of voiding, emptying, ejecting, or evacuating.
      [1913 Webster]

   2. (Eccl.) A ejection from a benefice.
      [1913 Webster]

   3. The state of being void; vacancy, as of a benefice which
      is without an incumbent.
      [1913 Webster]

   4. Evasion; subterfuge. [Obs.] --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

voidance
    n 1: the act of removing the contents of something [syn:
         emptying, voidance, evacuation]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "voidance":
   BM, abolishment, abolition, abrogation, annulment, bloody flux,
   bowel movement, cancel, canceling, cancellation, cassation,
   catharsis, cleaning out, clearance, clearing, countermand,
   counterorder, crap, defeasance, defecation, dejection, depletion,
   diarrhea, discharging cargo, drainage, draining, dysentery, egress,
   elimination, emptying, evacuation, excretion, exhausting,
   exhaustion, flux, invalidation, lientery, loose bowels, movement,
   nullification, off-loading, purgation, purge, recall, recantation,
   removal, renege, repeal, rescinding, rescindment, rescission,
   retraction, reversal, revocation, revoke, revokement, runs,
   setting aside, shit, shits, stool, suspension, trots, turistas,
   unloading, vacation, vacatur, venting, voiding, waiver, waiving,
   withdrawal, write-off