[1] : WordNet (r) 2.0

negate
     v 1: be in contradiction with syn: contradict, belie
     2: deny the truth of syn: contradict, contravene
     3: prove negative; show to be false syn: contradict ant: confirm
     4: make ineffective by counterbalancing the effect of; "her
        optimism neutralizes his gloom"; "this action will negate
        the effect of my efforts" syn: neutralize, neutralise,
         nullify
see also:
contradict belie contravene confirm neutralize neutralise 
nullify 

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

112 moby thesaurus words for "negate":
   abate, abnegate, abolish, abrogate, agree to disagree, annihilate,
   annul, be at cross-purposes, be contrary to, be unmoved,
   be unwilling, beg off, belie, blow sky-high, blow up, break,
   break off, bring to naught, bring to nothing, buffer,
   call into question, cancel, cancel out, challenge, clash, collide,
   come to nothing, conflict, contest, contradict, contravene,
   controvert, counter, counteract, counterbalance, countercheck,
   cross, decline, decline to accept, deflate, deny, differ,
   disaccord, disaffirm, disagree, disallow, disbelieve, disclaim,
   disconfirm, discredit, disprove, dissent, explode, expose,
   frustrate, gag on, gainsay, hold out against, impugn, invalidate,
   jangle, jar, jostle, misbelieve, mismatch, mismate, negativate,
   negative, neutralize, not admit, not believe, not buy, not consent,
   not hear of, not swallow, not think of, nullify, object, offset,
   oppugn, prove the contrary, puncture, quash, rebut, redress,
   refuse, refuse consent, refuse to admit, refuse to credit, reject,
   repeal, repudiate, resist entreaty, resist persuasion, revoke,
   say nay, say no, shake the head, show up, stand aloof, stultify,
   thwart, traverse, turn down, unbelieve, undercut, undo, vary,
   vitiate, void, vote nay, vote negatively

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