VOW is related to the Greek βεβαιώ (veveo)

[Neos]

The word vow (oath, assure) comes from the Latin voveo (I vow), which is related to the Greek verb βεβαιώ (to assure, to promise with certainty; veveo).
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In Greek.
α) βεβαιώ or βεβαιώνω: affirm, confirm, certify [veveo or veveono]
β) βεβαίωση: Affirmation, assurance, confirmation [veveosi]
γ) βεβαίως: adv. certainly, sure, of course [veveos]
δ) βέβαιος: certain, sure [veveos]

More: http://ewonago.blogspot.com/2008/07/vow.html