Vouch comes from Old French voucher ('to call, summon, invoke'), from Latin vocare ('to call'), from vox ('voice'). In current use it is a verb meaning "to assert or guarantee the truth, reliability, or worth of something". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. The historical chain includes Old French voucher, Latin vocare, and Latin vox. Related English forms include vouchsafe, vocal, vocation, and avouch. Derived forms include voucher, vouchee, and vouchment. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.