Unflagging (adjective)

Not showing signs of weariness or weakening.

Origin:

From the prefix un- meaning not and the word flagging.

Examples:

1. He had an unflagging energy that never seemed to fade.
2. She had an unflagging determination that was admirable.
3. The team had an unflagging spirit throughout the game.
4. The company had an unflagging commitment to customer satisfaction.
5. The athlete had an unflagging dedication to his training.