infallible
Americanadjective
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absolutely trustworthy or sure.
an infallible rule.
-
unfailing in effectiveness or operation; certain.
an infallible remedy.
-
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
Synonym Usage
See reliable.
Other Word Forms
Derived 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.
That is not to say humanity is infallible.
From Slate • May 28, 2026
For a while after that, they seemed totally infallible, a giant blue behemoth blocking out the light.
From BBC • May 6, 2026
Dimon also said Tuesday that he didn’t think the Fed was infallible and had made mistakes.
From The Wall Street Journal • Jan. 13, 2026
His pizzazz was a large measure of his appeal, along with his manufactured image as a shrewd businessman with a kingly touch and infallible judgment.
From Los Angeles Times • Jan. 4, 2026
In the United States the FBI, which often has to extract DNA in criminal cases, considers the test, when done with the latest technology, infallible.
From "Endgame" by Frank Brady
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.
