Vouch vs Undefined - What's the difference?

As a verb vouch

is to take responsibility for; to express confidence in; to witness; to obtest.

is warrant; attestation.

lacking a definition or value.

(es)

To take responsibility for; to express confidence in; to witness; to obtest.

To warrant; to maintain by affirmations; to attest; to affirm; to avouch.

* Atterbury

They made him ashamed to vouch the truth of the relation, and afterwards to credit it.

I can vouch that the match took place.

To back; to support; to confirm.

* Milton

Me damp horror chilled / At such bold words vouched with a deed so bold.

To call into court to warrant and defend, or to make good a warranty of title.

* Blackstone

He vouches' the tenant in tail, who ' vouches over the common vouchee.

(obsolete) To call; to summon.

* Sir T. Elyot

[They] vouch (as I might say) to their aid the authority of the writers.

To bear witness; to give testimony or full attestation.

* Jonathan Swift

He will not believe her until the elector of Hanover shall vouch for the truth of what she has affirmed.

To call as a witness.

* Dryden

Vouch the silent stars and conscious moon.

To assert; to aver; to declare.

(Shakespeare)

(es)

Warrant; attestation.

(wikipedia undefined) (-)

Lacking a definition or value.

(mathematics, computing) That does not have a meaning and is thus not assigned an interpretation.

The result of division by zero is undefined .

* defined