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indefatigable

[in-di-fat-i-guh-buh l] /ˌɪn dɪˈfæt ɪ gə bəl/
adjective
1.
incapable of being tired out; not yielding to fatigue; untiring.
Origin
1580-1590
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
Synonyms
tireless, inexhaustible, persevering.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for indefatigability

indefatigable

/ˌɪndɪˈfætɪɡəbəl/
adjective
1.
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
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Word Origin and History for indefatigability
indefatigable
1586 (implied in indefatigably), from Fr. indefatigable (15c.), from L. indefatigabilis "that cannot be wearied," from in- "not" + defatigare "to tire out," from de- "utterly, down, away" + fatigare "to weary" (see fatigue).
Online Etymology Dictionary, © 2010 Douglas Harper
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