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