infallible
Americanadjective
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absolutely trustworthy or sure.
an infallible rule.
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unfailing in effectiveness or operation; certain.
an infallible remedy.
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not fallible; exempt from liability to error, as persons, their judgment, or pronouncements.
an infallible principle.
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Roman Catholic Church. immune from fallacy or liability to error in expounding matters of faith or morals by virtue of the promise made by Christ to the Church.
noun
adjective
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not fallible; not liable to error
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not liable to failure; certain; sure
an infallible cure
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completely dependable or trustworthy
noun
Related Words
See reliable.
Other Word Forms
Etymology
Origin of infallible
First recorded in 1375–1425; late Middle English word from Medieval Latin word infallibilis. See in- 3, fallible
Explanation
"Fallible" means capable of making mistakes — or, easier to remember — capable of failing. Infallible means exactly the opposite — incapable of failing. This word is often used to describe human capacity for error — no one is infallible. And yet, we are able to be infallible in certain ways: children are infallibly curious, teenagers infallibly hungry. Interestingly, infallible derives from the Latin in- "not" + fallere "deceive." When did making a mistake and deception become the same thing?
Vocabulary lists containing infallible
The Vocabulary.com Top 1000
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ASVAB Word Knowledge
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"The Odyssey" by Homer, Books 1–7
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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.
A lapse in judgment has sent the previously infallible industry visionary, with Agnes in tow, into self-imposed, self-described exile on Maui, where the Hopkinses have built a showstopper of a house.
From The Wall Street Journal • Apr. 17, 2026
But it does make clear that AI isn’t magic, nor are those who are making and marketing it infallible.
From Los Angeles Times • Mar. 26, 2026
They are never infallible or immune to misjudgment.
From Slate • Feb. 16, 2026
They aren't infallible but they will increase the hassle factor for criminals.
From BBC • Feb. 7, 2026
Dr. Montague was confirmed, made infallible; under the sign which pointed the way to Route 39 was another sign saying: ASHTON, 121 MILES.
From "The Haunting of Hill House" by Shirley Jackson
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.
