vouch

The story

1. Old French · calque ofvoucher a garant
2. Proto-Indo-European · derived from*wekʷ-“to sound out; to speak”
3. Latin · derived fromvocāre“to call, summon; to call upon, invoke; to designate, name; to bring or put (into a condition or state”
4. Vulgar Latin · derived from*vocicāre
5. Old French · derived fromvocher, voucher, vochier“to call, summon; to claim; to call upon, invoke; to denounce”
6. Anglo-Norman · derived fromvocher, voucher, woucher
7. Middle English · inherited fromvouchen“to call, summon; to provide; to make available, proffer; to affirm, declare formally”
8. English todayvouch

The verb is derived from Middle English vouchen (“to call, summon; to provide; to make available, proffer; to affirm, declare formally”) [and other forms], from Anglo-Norman vocher, voucher, woucher, and Old French vocher, voucher, vochier (“to call, summon; to claim; to call upon, invoke; to denounce”) [and other forms], from Vulgar Latin *vocicāre, derived from Latin vocāre (“to call, summon; to call upon, invoke; to designate, name; to bring or put (into a condition or state”), ultimately from Proto-Indo-European *wekʷ- (“to sound out; to speak”). Verb sense 8.1 (“to summon (someone) into court to establish a warranty of title to land”) in the form vouch to warrant or vouch to warranty is a calque from Anglo-Norman and Old French voucher a garant. The noun is derived from the verb.