vouch 
(vouch)
(vouch)v. vouched, vouch·ing, vouch·es
v.intr.
1. To give personal assurances or a guarantee: vouch for an old friend's trustworthiness.
2. To constitute supporting evidence; give substantiation: a candidate whose strong record vouches for her ability.
v.tr.
Archaic
Archaic
1. To substantiate by supplying evidence; prove: "When any particular matter of fact is vouched by the concurrent testimony of unsuspected witnesses, there our assent is also unavoidable" (John Locke).
2. Law To summon (someone) as a witness to give warranty of title.
3. To refer to (an authority, for example) in support or corroboration; cite.
4. To assert; declare.
n.
Obsolete
Obsolete
A declaration of opinion; an assertion.
[Middle English vouchen, to summon to court, warrant, from Anglo-Norman voucher, probably from Vulgar Latin *voticāre, alteration of Latin vocitāre, frequentative of vocāre, to call; see wekw- in the Appendix of Indo-European roots.]