fallacy
Americannoun
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a deceptive, misleading, or false notion, belief, etc..
That the world is flat was at one time a popular fallacy.
- Synonyms:
- misapprehension, delusion, misconception
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a misleading or unsound argument.
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deceptive, misleading, or false nature; erroneousness.
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Logic. any of various types of erroneous reasoning that render arguments logically unsound.
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Obsolete. deception.
noun
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an incorrect or misleading notion or opinion based on inaccurate facts or invalid reasoning
-
unsound or invalid reasoning
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the tendency to mislead
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logic an error in reasoning that renders an argument logically invalid
Etymology
Origin of fallacy
First recorded in 1350–1400; from Latin fallācia “a trick, deceit,” from fallāc- (stem of fallāx ) “deceitful” + -ia -y 3; replacing Middle English fallace, from Middle French
Explanation
A fallacy is a misleading argument or belief based on a falsehood. If you oppose state testing in schools, you think it is a fallacy that educational quality can be measured by standardized tests. Fallacy comes from the Latin fallacia, for deceit. It technically means a flaw in an argument that makes it deceptive or misleading. In poetry, the "pathetic fallacy" is the false idea that things like rocks or stars have human feelings (pathos). Fallacy can also be used more generally for any false statement or idea. Some synonyms are misconception and error.
Vocabulary lists containing fallacy
Argumentative Writing
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TEKS ELAR Academic Vocabulary List (5th-7th grades)
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Power Suffix: -acy
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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.
"This is the sunk cost fallacy," he said, adding that "it keeps the addictive behaviour loop".
From Barron's • May 31, 2026
Loss aversion, sunk-cost fallacy and herd behavior — all of it kicks in during a drawdown.
From MarketWatch • May 12, 2026
“There’s this fallacy that companies were lowering the bar,” she says.
From The Wall Street Journal • Nov. 13, 2025
The promise is that we can shape behavior; the fallacy is that the power rarely reaches beyond cosmetic concessions.
From Salon • Aug. 28, 2025
Naturally, I don’t subscribe to the obvious fallacy that every society promptly adopts every innovation that would be useful for it.
From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond
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.