To tell someone something positively to dispel any doubts they may have. She assured him that the project would be completed on time.
To make something certain to happen. The new contract assures the company's future success.
To make someone feel confident about something. He assured her of his support during the difficult times.
To insure, especially a person's life, so that payment will be made in the event of death or loss. He assured his life for £250,000 before setting sail.