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: Webster's Revised Unabridged Dictionary (1913)