tire·less (tīr'lĭs) adj. Not yielding to fatigue; untiring or indefatigable. tire'less·ly adv., tire'less·ness n.
Synonyms: These adjectives mean having or showing a capacity for prolonged and laborious effort: a tireless worker; an indefatigable advocate of human rights; unflagging pursuit of excellence; untiring energy; an unwearied researcher; a weariless defender of freedom of the press.