Dictionary.com
Thesaurus.com
Showing results for indefatigable. Search instead for indefatigableness.
Synonyms

indefatigable

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

adjective

  1. incapable of being tired out; not yielding to fatigue; untiring.

    Synonyms:
    persevering, inexhaustible, tireless

indefatigable British  
/ ˌɪndɪˈfætɪɡəbəl /

adjective

  1. unable to be tired out; unflagging

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Word Forms

  • indefatigability noun
  • indefatigableness noun
  • indefatigably adverb

Etymology

Origin of indefatigable

1580–90; < Latin indēfatīgābilis untiring, equivalent to in- in- 3 + dēfatīgā ( re ) to tire out ( de-, fatigue ) + -bilis -ble

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.

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

It’s a rollicking animal story; it’s also a tale of indefatigable love.

From The Wall Street Journal • Nov. 7, 2025

Underlings have long marveled at his indefatigable work ethic.

From Los Angeles Times • Oct. 30, 2025

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