nullify

(verb) declare invalid. Synonyms: invalidate, annul, quash, void, avoid. Examples: "The contract was annulled." "Void a plea."

(verb) show to be invalid. Synonyms: invalidate.

(verb) make ineffective by counterbalancing the effect of. Synonyms: neutralize, neutralise, negate. Examples: "Her optimism neutralizes his gloom." "This action will negate the effect of my efforts."