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  1. incapable of being tired out; not yielding to fatigue; untiring.
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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


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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for indefatigability

Historical Examples

  • No painter ever copied himself with more constancy and indefatigability.


    Alys Eyre Macklin

  • It is because of my own indefatigability in talking about talk about talk that they made me a Knight.

  • Your mastery of the language, and your indefatigability, would make you infinitely useful in any of these departments.

  • Owing to the indefatigability of collectors and their persistent and tempting offers, many have left their old homes.

  • At the Westminster election, his indefatigability against the ministerial favourite came amply into play.

British Dictionary definitions for indefatigability


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

Word Origin and History for indefatigability


1630s, from indefatigable + -ity.

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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).

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Online Etymology Dictionary, © 2010 Douglas Harper