voucher

Short definition from Wiktionary

Noun

1. 1
   A piece of paper or other token that entitles the holder to a discount, or that can be exchanged for goods and services.
2. 2
   A receipt.
3. 3
   One who or that which vouches.
4. 4
   A copy of a published advertisement sent by the agency to the client as proof of publication.
5. 5
   A mechanical device used in shops for automatically registering the amount of money drawn.

Verb

1. 1
   To establish the authenticity of; to vouch for.
2. 2
   To provide a vouch for (an expenditure).
3. 3
   To provide (a beneficiary) with a voucher.