(a.) Incapable of being fatigued; not readily exhausted; unremitting in labor or effort; untiring; unwearyingly; not yielding to fatigue; as, indefatigable exertions, perseverance, application.

abiding ardent assiduous constant continuing continuous determined diligent dogged enduring energetic faithful fervent hard hardworking immutable inalterable indomitable industrious inexhaustible insistent invincible laborious lasting loyal never idle never-tiring obstinate painstaking patient patient as Job permanent perseverant persevering persistent persisting pertinacious plodding plugging preoccupied rapt relentless remaining resolute sedulous single-minded sleepless slogging stable staying steadfast steady sticking strenuous stubborn sustained tenacious tireless unabating unceasing unconquerable undaunted undiscouraged undrooping undying unfailing unfaltering unflagging unflinching unintermitting uninterrupted unnodding unrelaxing unrelenting unremitting unsleeping unsparing unswerving untiring unwavering unwearied unwearying unwinking utterly attentive vehement vigorous weariless zealous