Origin: ME avouchen < OFr avochier, to affirm positively < L advocare: see advocate
See avouch in American Heritage Dictionary 4
transitive verb a·vouched, a·vouch·ing, a·vouch·es
Origin: Middle English avouchen, to cite as a warrant
Origin: , from Old French avochier
Origin: , from Latin advocāre, to summon; see advocate.
Learn more about avouch