vouch

To give personal assurances or a guarantee.

To constitute supporting evidence; give substantiation.

To substantiate by supplying evidence; prove.

To summon (someone) as a witness to give warranty of title.

To refer to (an authority, for example) in support or corroboration; cite.

To assert; declare.

A declaration of opinion; an assertion.

Approving or supporting warrant; confirmation; attestation.

To call to witness.

To declare; assert; affirm; attest; avouch.