Antonyms for ratify

affirm, authorize:

destroy, refuse, invalidate, disagree, Disaffirm, deny, disprove, veto, revoke, disapprove, reject, contradict, renounce, disallow, oppose.

noun:

destroy, neglect, deny, proscribe, overlook, console, upset, reject, rebuff, refuse, forbid, negative, disapprove, ban, decline, overthrow, interdict, condole with, spurn, shatter, prohibit, illegalize, unsettle, disallow, turn down, enjoin, disregard, weaken, rebut, shake, ignore, veto.