indefatigable

adjective

in·​de·​fat·​i·​ga·​ble ˌin-di-ˈfa-ti-gə-bəl 

: incapable of being fatigued : untiring

an indefatigable worker

indefatigability

ˌin-di-ˌfa-ti-gə-ˈbi-lə-tē 

noun

indefatigableness

ˌin-di-ˈfa-ti-gə-bəl-nəs 

noun

indefatigably

ˌin-di-ˈfa-ti-gə-blē 

adverb

Synonyms

• meticulous
• tireless
• relentless
• untiring
• unflagging
• conscientious
• inexhaustible
• vigorous
• active
• energetic
• diligent
• intense

Examples of indefatigable in a Sentence

a person of indefatigable patience

an indefatigable laborer who can work from sunrise to sunset

Recent Examples on the Web

However, her husband is the indefatigable former Buffalo Bills coach Marv Levy, and the man doesn’t shrink from a challenge. —Tim Graham, New York Times, 1 Aug. 2025

Shortly after the devastation, Montag saw music from her debut album Superficial go viral and find new life (spurred in large part by Pratt’s indefatigable promotional skills) with the help of A-list stars and countless TikTok users. —Chris Gardner, HollywoodReporter, 24 July 2025

The indefatigable Curtis Sliwa ran uncontested in the Republican primary. —Jill Goldsmith, Deadline, 14 July 2025

But at 83, the indefatigable Beatle is indeed taking another spin around the U.S. with his Got Back tour. —Melissa Ruggieri, USA Today, 11 July 2025

Word History

Etymology

Middle French, from Latin indefatigabilis, from in- + defatigare to fatigue, from de- + fatigare to fatigue

First Known Use

1608, in the meaning defined above

Kids Definition

indefatigable

adjective

in·​de·​fat·​i·​ga·​ble ˌin-di-ˈfat-i-gə-bəl 

: capable of working a long time without tiring : tireless

an indefatigable teacher

indefatigably

-blē 

adverb