To assert, aver, or declare (something).
To provide evidence or proof.
To back, confirm, or support (someone or something) with credible evidence or proof.
To call on (someone) to be a witness to something.
To affirm or warrant the correctness or truth of (something); also, to affirm or warrant (the truth of an assertion or statement).
To bear witness or testify; to guarantee or sponsor.
To cite or rely on (an authority, a written work, etc.) in support of one's actions or opinions.
To bear witness or testify to the nature or qualities (of someone or something).
In full vouch to warrant or vouch to warranty: to summon (someone) into court to establish a warranty of title to land.
Followed by over: of a vouchee (a person summoned to court to establish a warranty of title): to summon (someone) to court in their place.
To express confidence in or take responsibility for (the correctness or truth of) something.
An assertion, a declaration; also, a formal attestation or warrant of the correctness or truth of something.