negate

Synonyms: abate abolish abrogate annihilate annul belie blackball break with cancel cancel out controvert countercheck cross deny ding disaffirm disallow disprove dump fly in the face of frustrate gainsay impugn invalidate kill negative neutralize nullify oppose put down quash rebut redress refute repeal rescind retract reverse revoke stonewall traverse turn down turn thumbs down undo vitiate void

Antonyms: allow approve permit