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

Princess Anne is the second child and only daughter of the late Queen Elizabeth and Prince Philip, and has followed in her parents' footsteps with an indefatigable devotion to royal duty. —Janine Henni, People.com, 8 Aug. 2025

But the new president is known to be indefatigable and is already familiar with the inner workings of the Academy and the Oscars, so she is expected to be able to hit the ground running. —Scott Feinberg, HollywoodReporter, 31 July 2025

In other words, Cyndi has remained Cyndi – indefatigable, loyal and bracingly authentic. —Melissa Ruggieri, USA Today, 26 July 2025

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

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