To show to be true by demonstration or evidence; to confirm the truth or authenticity of; to substantiate. Of things, or in passive.

To guarantee as true, make oneself answerable for (a statement). With noun as object: To vouch for the truth of (an opinion).

transitive. To warrant, vouch for; to aver, confirm. Obsolete.

To show forth evidence of or as to (an object of allegiance) by faithful speech or conduct; to be a witness for. Also with cognate object. Now rare…

transitive. To provide evidence or authority for, or corroboration of, (a statement, etc.); to bear out, substantiate.

To vouch for. Obsolete. rare.

intransitive. With for. Of things: To supply evidence or assurance of (some fact).