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 of indefatigable

• 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

By nineteen, she was married with two children, and discovering that an indefatigable work ethic meant nothing when a man could forbid you from working. —Dan Piepenbring, Harpers Magazine, 24 Mar. 2026

The indefatigable musician was on hand to plug his upcoming debut solo album, Honora, which is due out on Friday (March 27). —Gil Kaufman, Billboard, 24 Mar. 2026

The Comeback cast features new, starry additions like Andrew Scott, Jane Fonda, Abbi Jacobson and John Early, in addition to returning regulars Dan Bucatinsky (also an executive producer), Laura Silverman as indefatigable doc producer Jane and Damian Young as Cherish’s beleaguered husband, Mark. —Chris Gardner, HollywoodReporter, 18 Mar. 2026

Smith has never been the indefatigable champion of free enterprise imagined by his acolytes. —Literary Hub, 9 Mar. 2026

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