avouch

Etymology

From Old French avouchier, from Latin advocāre, present active infinitive of advocō. Doublet of advocate, advoke, and avow.

verb

1. To declare freely and openly; to assert.
2. To acknowledge deliberately; to admit; to confess; to sanction.
3. To confirm or verify, to affirm the validity of.
   As a great public document, addressed to the whole Christian world by him who aspired to be the first ecclesiastic, we might be disposed to question its authenticity, if it were not avouched by the full evidence in its favour and its agreement with all the events of the period. 1855, Henry Hart Milman, History of Latin Christianity, London: John Murray, Volume 2, Book 4, Chapter 7, p. 159
4. To appeal to; to cite or claim as authority.

noun

1. (obsolete) evidence; declaration