assurance

This term conveys a sense of certainty and security, whether it is an external promise made to another person or an internal state of confidence. It differs from a simple promise by implying a stronger, more formal commitment designed to eliminate anxiety or doubt.

In British English, the word is used specifically in a financial context to describe a life insurance policy that is guaranteed to pay out, as opposed to insurance which only pays if a specific event occurs. This creates a distinct semantic divide between the general sense of confidence and the technical legal sense of a guaranteed payout.