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 formsin·de·fat·i·ga·bil·i·ty, in·de·fat·i·ga·ble·ness, nounin·de·fat·i·ga·bly, adverb

Synonyms for indefatigable Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for indefatigable

Contemporary Examples of indefatigable

Historical Examples of indefatigable

  • 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.


    Samuel Smiles

  • He was a man of indefatigable activity, and was constantly on the move.


    Samuel Smiles

British Dictionary definitions for indefatigable



unable to be tired out; unflagging
Derived Formsindefatigability or indefatigableness, nounindefatigably, adverb

Word Origin for indefatigable

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

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