voucher
1. vouch.er \'vau.-ch*r\ n 1: an act of vouching 2a: a piece of supporting evidence : PROOF 2b: a documentary record of a business transaction 2c: a written affidavit or authorization 2. voucher vt : to establish the authenticity of; esp : to certify by a voucher 3. voucher n : one that guarantees : SURETY