Source : Webster's Revised Unabridged Dictionary (1913)

Vouch \Vouch\, v. t. [imp. & p. p. {Vouched}; p. pr. & vb. n.
   {Vouching}.] [OE. vouchen, OF. vochier to call, fr. L. vocare
   to call, fr. vox, vocis, voice. See {Voice}, and cf.
   {Avouch}.]
   1. To call; to summon. [Obs.]

            [They] vouch (as I might say) to their aid the
            authority of the writers.             --Sir T.
                                                  Elyot.

   2. To call upon to witness; to obtest.

            Vouch the silent stars and conscious moon. --Dryden.

   3. To warrant; to maintain by affirmations; to attest; to
      affirm; to avouch.

            They made him ashamed to vouch the truth of the
            relation, and afterwards to credit it. --Atterbury.

   4. To back; to support; to confirm; to establish.

            Me damp horror chilled At such bold words vouched
            with a deed so bold.                  --Milton.

   5. (Law) To call into court to warrant and defend, or to make
      good a warranty of title.

            He vouches the tenant in tail, who vouches over the
            common vouchee.                       --Blackstone.

   Syn: To obtest; declare; affirm; attest; warrant; confirm;
        asseverate; aver; protest; assure.