voucher (n.)

early 14c., "summon into court to prove a title," from Anglo-French voucher, Old French vocher "to call, summon, invoke, claim," probably from Gallo-Roman *voticare, metathesis of Latin vocitare "to call to, summon insistently," frequentative of Latin vocare "to call, call upon, summon," which is related to vox (genitive vocis) "voice" (from PIE root *wekw- "to speak"). Meaning "guarantee to be true or accurate" is first attested 1590s. Related: Vouched; vouching.