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[in-di-fat-i-guh-buh l] /ˌɪn dɪˈfæt ɪ gə bəl/
incapable of being tired out; not yielding to fatigue; untiring.
Origin of indefatigable
1580-90; < Latin indēfatīgābilis untiring, equivalent to in- in-3 + dēfatīgā(re) to tire out (see de-, fatigue) + -bilis -ble
Related forms
indefatigability, indefatigableness, noun
indefatigably, adverb
tireless, inexhaustible, persevering. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for indefatigable
Contemporary Examples
Historical Examples
  • He was as indefatigable in politeness, as his wife had been in her regimental duties.

  • indefatigable as they were in their labours, they could not command success.

  • Quinn was fearless, daring, indefatigable; but Quinn was not Ferry.

    The Cavalier George Washington Cable
  • Harvey was as indefatigable a labourer as any we have named.

    Self-Help Samuel Smiles
  • The fame of Claude Lorraine is partly explained by his indefatigable industry.

    Self-Help Samuel Smiles
British Dictionary definitions for indefatigable


unable to be tired out; unflagging
Derived Forms
indefatigability, indefatigableness, noun
indefatigably, adverb
Word Origin
C16: from Latin indēfatīgābilis, from in-1 + dēfatīgāre, from fatīgāre to tire
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
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Word Origin and History for indefatigable

1580s (implied in indefatigably), from French indefatigable (15c.), from Latin indefatigabilis "that cannot be wearied," from in- "not" (see in- (1)) + defatigare "to tire out," from de- "utterly, down, away" + fatigare "to weary" (see fatigue).

Online Etymology Dictionary, © 2010 Douglas Harper
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