surer

adjective

• Physically secure and certain, non-failing, reliable.

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

• 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."

• Certain to act or be a specified way.

  "Be sure to lock the door when you leave."

• Free from danger; safe; secure.
• Betrothed; engaged to marry.