Russian-English translations for заверить

• assure
  I assure you that the program will work smoothly when we demonstrate it to the client.
  He assured of his commitment to her happiness.
• attest
  When will the appraiser attest the date of the painting?
  You must attest your will in order for it to be valid.
  Her fine work attested her ability.
• certify
  These blankets have been certified as fireproof.
• witness
  She can bear witness, since she was there at the time.
  As a witness to the event, I can confirm that he really said that.
  The witness for the prosecution did not seem very credible.