vouch·er /ˈvaʊʧɚ/
  證人,保證人,證明者,憑證,憑單(vt.)證實…的可靠性
  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.
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  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]