voucher

noun

Pronunciation: /ˈvaʊt͡ʃə(ɹ)/

Etymology: From vouch + -er. The verb is from the noun.

A piece of paper or other token that entitles the holder to a discount, or that can be exchanged for goods and services.
“a voucher for a free kettle”
“This voucher entitles the bearer to a 20% discount on frozen goods.”
A receipt.
One who or that which vouches.
“To the fashionable world he cannot be a stranger […] and his having married a sister of the Duke of Leeds is a voucher for my assertion.”
“She is my sister—my own father’s daughter. Well; why do I believe it? The other day I had not so much as heard the remotest rumor of her existence; and what has since occurred to change me? What so new and incontestable vouchers have I handled? None at all.”
A copy of a published advertisement sent by the agency to the client as proof of publication.
“Most agencies also have a vouchers department. It is its responsibility to obtain a copy of every advertisement that appears in print. It supplies the accounts department with the relevant newspaper or magazine, which is affixed to the agency's invoice for the space.”
A mechanical device used in shops for automatically registering the amount of money drawn.

Etymology: From vouch + -er. The verb is from the noun.