indefatigable

[in-di-fat-i-guh-buhl] / ˌɪn dɪˈfæt ɪ gə bəl /

ADJECTIVE

untiring

Synonyms

STRONGEST

assiduous diligent dogged energetic inexhaustible painstaking relentless tireless unflagging unwavering vigorous

WEAK

active bound and determined dead set on determined hell-bent industrious ironclad nose to grindstone patient persevering persistent pertinacious sedulous steadfast stop-at-nothing strenuous unfaltering unflinching unremitting unwearied unwearying

Antonyms

STRONGEST

changing idle inactive indifferent lazy lethargic negligent tired wavering

WEAK

fatigued weary

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Celebrate the French Open by watching its greatest champion, Rafael Nadal, endure endless pain and injury in his indefatigable quest for tennis glory.

From Los Angeles Times • May 18, 2026

But an indefatigable Volkanovski's agility and relentless striking eventually wore down his flagging challenger, who was unable to land a knockout in the final round.

From Barron's • Feb. 1, 2026

Mr. Dooley is also a discerning and indefatigable researcher.

From The Wall Street Journal • Jan. 21, 2026

They deserve our support, as do a slew of writers, such as the indefatigable Heather Cox Richardson and Ruth Ben-Ghiat, who publish via Substack.

From Salon • Jul. 5, 2025

Blanching at the thought of the indefatigable Lawrence pestering Fosdick in person, Weaver responded sharply, “I don’t see it.”

From "Big Science" by Michael Hiltzik

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