Avouch, v. t. [imp. & p. p. Avouched (p. pr. & vb. n. Avouching.]
Etymology: [OF. avochier, LL. advocare to recognize the existence of a thing, to advocate, fr. L. advocare to call to; ad + vocare to call. Cf. Avow to declare, Advocate, and see Vouch, v. t.]
1. To appeal to; to cite or claim as authority. [Obs.] They avouch many successions of authorities. Coke.
2. To maintain a just or true; to vouch for. We might be disposed to question its authencity, it if were not avouched by the full evidence. Milman.
3. To declare or assert positively and as matter of fact; to affirm openly. If this which he avouches does appear. Shak. Such antiquities could have been avouched for the Irish. Spenser.
4. To acknowledge deliberately; to admit; to confess; to sanction. Thou hast avouched the Lord this day to be thy God. Deut. xxvi. 17.
1 other Webster entry under this spelling
Avouch, n.
Evidence; declaration. [Obs.] The sensible and true avouch Of mine own eyes. Shak.
Shades of meaning
Fernald has no entry of its own for avouch; he lists it under avow, state.
Where he writes about it:
Avow and avouch take a direct object; aver is followed by a conjunction: a man avows his faith, avouches a deed, avers that he was present. — from avow