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gain·say
ˌɡānˈsā/
verb
formal
verb: gainsay; 3rd person present: gainsays; past tense: gainsaid; past participle: gainsaid; gerund or present participle: gainsaying
  1. deny or contradict (a fact or statement).
    “the impact of the railroads cannot be gainsaid”
    synonyms: deny, dispute, disagree with, argue with, dissent from, contradict, repudiate, challenge,oppose, contest, counter, controvert, rebut

    “it was difficult to gainsay his claim”
    antonyms: confirm
    • speak against or oppose (someone).
Origin
Middle English: from obsolete gain- ‘against’ + say.