Voucher
Voucher , noun
1.
One who vouches, or gives witness or full attestation, to anything.
Will his vouchers vouch him no more?
The great writers of that age stand up together as vouchers for one another's reputation.
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.
(a) (Law) 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)
(Law) 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
4.
A document attesting to a credit against certain defined expenditures; a receipt for prepayment; -- often used in pre-arranged travel plans, to provide evidence of pre-payment of the cost of lodging, transportation, or meals.