indefatigable
Americanadjective
adjective
Other Word Forms
Etymology
Origin of indefatigable
1580–90; < Latin indēfatīgābilis untiring, equivalent to in- in- 3 + dēfatīgā ( re ) to tire out ( see de-, fatigue) + -bilis -ble
Explanation
Someone who is indefatigable can go on for a very long time without becoming tired. You might not be so happy to have an indefatigable guide on your walking trip––you'll have blisters, but she'll see no reason not to keep going. Indefatigable comes from Latin indefatigabilis, formed from the prefix in- "not" plus defatigare "to tire out." Here the prefix de- means "entirely." You can remember the root fatigare because it sounds so much like the English fatigue.
Vocabulary lists containing indefatigable
Animal Farm
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The Scarlet Letter
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The Haunting of Hill House
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
But thanks to Reid’s indefatigable charisma, this vampire sidesteps the resentment millions hold for real-life bloodsuckers by inviting us behind the velvet curtain.
From Salon ● Jun. 13, 2026
At first, Epstein, an indefatigable social networker, was anxious over whether Tisch liked him or not.
From The Wall Street Journal ● Feb. 12, 2026
But an indefatigable Volkanovski's agility and relentless striking eventually wore down his flagging challenger, who was unable to land a knockout in the final round.
From Barron's ● Feb. 1, 2026
Underlings have long marveled at his indefatigable work ethic.
From Los Angeles Times ● Oct. 30, 2025
It was a monumental irony: The man famous as the indefatigable orator of independence in the Continental Congress was obliged to remain silent in the legislative councils of the new government.
From "Founding Brothers: The Revolutionary Generation" by Joseph J. Ellis
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
