[1] : The Collaborative International Dictionary of English v.0.48

nullify \nul"lify\, v. t. imp.  p. p. nullified; p. pr. 
   vb. n. nullifying. l. nullificare; nullus none + -ficare
   in comp. to make. see null, a., and -fy.
   to make void; to render invalid; to deprive of legal force or
   efficacy.
   1913 webster

         such correspondence would at once nullify the
         conditions of the probationary system.   --i. taylor.
   1913 webster

   syn: to abrogate; revoke; annul; repeal; invalidate; cancel.
        see abolish.
        1913 webster
see also:
nullified nullifying null -fy abolish 

[2] : WordNet (r) 2.0

nullify
     v 1: declare invalid; "the contract was annulled"; "void a plea"
          syn: invalidate, annul, quash, void, avoid
          ant: validate
     2: show to be invalid syn: invalidate ant: validate
     3: make ineffective by counterbalancing the effect of; "her
        optimism neutralizes his gloom"; "this action will negate
        the effect of my efforts" syn: neutralize, neutralise,
         negate
     also: nullified
see also:
invalidate annul quash void avoid validate 
neutralize neutralise negate nullified 

[3] : Moby Thesaurus II by Grady Ward, 1.0

86 moby thesaurus words for "nullify":
   abate, abjure, abolish, abrogate, absolve, annihilate, annul,
   assert the contrary, belie, bring to naught, bring to nothing,
   buffer, cancel, cancel out, come to nothing, compensate, confine,
   contest, contradict, contravene, controvert, counter, counteract,
   counterbalance, countermand, counterorder, countervail, cross,
   declare a moratorium, deny, disaffirm, disallow, disannul, disavow,
   disclaim, disown, disprove, dispute, do away with, forswear,
   frustrate, gainsay, impugn, invalidate, join issue upon, limit,
   make void, negate, negativate, negative, neutralize, not accept,
   not admit, obliterate, offset, oppose, override, overrule, quash,
   recall, recant, refuse to admit, refute, renege, renounce, repeal,
   repudiate, rescind, restrict, retract, reverse, revoke, set aside,
   stultify, suspend, take back, take issue with, thwart, undo,
   vacate, vitiate, void, waive, wipe out, withdraw, write off

Nullify >> N Words
Nullify, definition of term: Nullify
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