avow
Avow (verb) means to state something openly and confidently, admitting it is true.
Etymology
Came into English from Middle English avowen, from Old French avouer, from Latin advocare, meaning “to call to, call upon, hence to call as a witness, defender, patron, or advocate”, itself from ad, “to”, and vocare, “to call”. It is a doublet of advoke, avouch and advocate, but is not related to vow.