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