Unfailing (adjective)

Never failing or likely to fail; always dependable; constant; steady.

Origin:

From un- (not) + failing (to fail, to be unsuccessful).

Examples:

1. The nurse has an unfailing dedication to her patients.
2. His unfailing optimism always lifted the team's spirits.
3. She had an unfailing memory and never forgot a face or a name.
4. The machine had an unfailing performance, it never broke down.
5. The clock had an unfailing accuracy and was always on time.