Untiring (adjective)

1. Not causing fatigue or exhaustion.
2. Endless or persistent in effort.

Origin:

Derived from the word 'tiring' meaning causing fatigue or exhaustion.

Examples:

1. The untiring athlete continued to compete despite many injuries.
2. The untiring teacher never gave up on her students.
3. The untiring volunteer worked tirelessly to help those in need.
4. The untiring parent never stopped supporting their children.
5. The untiring activist never wavered in their fight for justice.