assure

verb4

1. •
   to tell someone something in a way that makes them certain it is true or can be trusted

   • I assure you that the program will work smoothly when we demonstrate it to the client.
   • He assured of his commitment to her happiness.
2. •
   To reassure.
3. •
   To make sure and secure; ensure.
4. •
   (no longer used) To guarantee, promise (to do something).

   • That as a law for euer should endure; / Which to obserue in word of knights they did assure. — 1590