Affirm or assert.
assert, maintain, state, aver, affirm, contend, argue, insist, hold, profess, move, claim, allege, avow, vow, swear, attest, testify, certifyView synonyms
- ‘We might be disposed to question its authenticity, it if were not avouched by the full evidence.’
- ‘Paulina and her friends being gone, I scarce could avouch that I had really seen them.’
- ‘Ask Wall Street and they would enthusiastically avouch that they are quite up to the task - more than able and willing.’
Late 15th century: from Old French avochier, from Latin advocare summon in defense from ad- to + vocare to call.