surest

adjective

1. 1

   Physically secure and certain, non-failing, reliable.

   “This investment is a sure thing.   The bailiff had a sure grip on the prisoner's arm.”

2. 2

   Certain in one's knowledge or belief.

   “He was sure she was lying.   I am sure of my eventual death.   John was acting sure of himself but in truth had doubts.”

3. 3

   Certain to act or be a specified way.

   “Be sure to lock the door when you leave.”

4. 4

   Free from danger; safe; secure.

5. 5

   Betrothed; engaged to marry.