Source : Webster's Revised Unabridged Dictionary (1913)

Voucher \Vouch"er\, n.
   1. One who vouches, or gives witness or full attestation, to
      anything.

            Will his vouchers vouch him no more?  --Shak.

            The great writers of that age stand up together as
            vouchers for one another's reputation. --Spectator.

   2. A book, paper, or document which serves to vouch the truth
      of accounts, or to confirm and establish facts of any
      kind; also, any acquittance or receipt showing the payment
      of a debt; as, the merchant's books are his vouchers for
      the correctness of his accounts; notes, bonds, receipts,
      and other writings, are used as vouchers in proving facts.

   3. (Law)
      (a) The act of calling in a person to make good his
          warranty of title in the old form of action for the
          recovery of lands.
      (b) The tenant in a writ of right; one who calls in
          another to establish his warranty of title. In common
          recoveries, there may be a single voucher or double
          vouchers. --Blackstone.

Source : WordNet®

voucher
     n 1: someone who vouches for another or for the correctness of a
          statement [syn: {verifier}]
     2: a document that serves as evidence of some expenditure
     3: a negotiable certificate that can be detached and redeemed
        as needed [syn: {coupon}]