vouch (v.)

• acknowledge
• affirm
• allege
• asseverate
• assure
• attest
• aver
• avouch
• avow
• book
• certify
• confirm
• corroborate
• countersign
• depone
• depose
• disclose
• endorse
• guarantee
• pledge
• plight
• position
• predicate
• promise
• proposition
• protest
• prove
• say
• sponsor
• stance
• stand
• substantiate
• support
• swear
• testify
• troth
• underwrite
• uphold
• verify
• vow
• warrant
• witness
• word