undersign (v.)

• accept
• accredit
• affirm
• approve
• assure
• attest
• authenticate
• authorize
• autograph
• back
• bond
• certify
• confirm
• cosign
• countersign
• endorse
• ensure
• guarantee
• initial
• insure
• notarize
• pass
• permit
• ratify
• sanction
• seal
• second
• secure
• sign
• sponsor
• support
• underwrite
• validate
• visa
• vise
• warrant