Source : WordNet®

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}]