Webster's Revised Unabridged Dictionary · 1913

Indefatigable

Indefatigable (in`de*fat"i*gȧ*b'l) , adjective

[Latin indefatigabilis: compare Old French indefatigable. See In- not, and Defatigable, and compare Infatigable.]

Incapable of being fatigued; not readily exhausted; unremitting in labor or effort; untiring; unwearying; not yielding to fatigue; as, indefatigable exertions, perseverance, application.
A constant, indefatigable attendance. — South
Upborne with indefatigable wings. — Milton