impenetrable
Americanadjective
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not penetrable; that cannot be penetrated, pierced, entered, etc.
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inaccessible to ideas, influences, etc.
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incapable of being understood; inscrutable; unfathomable.
an impenetrable mystery.
- Synonyms:
- hidden, obscure, mysterious, incomprehensible
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Physics. possessing impenetrability.
adjective
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incapable of being pierced through or penetrated
an impenetrable forest
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incapable of being understood; incomprehensible
impenetrable jargon
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incapable of being seen through
impenetrable gloom
-
not susceptible to ideas, influence, etc
impenetrable ignorance
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physics (of a body) incapable of occupying the same space as another body
Other Word Forms
Etymology
Origin of impenetrable
1425–75; late Middle English impenetrabel < Latin impenetrābilis. See im- 2, penetrable
Explanation
Impenetrable describes something that's impossible to get through. Whether it's a brick wall or a difficult reading passage, something impenetrable won't let you in. Impenetrable comes from the Latin impenetrabilis, meaning "not to put or get into, enter into." Impenetrable, the adjective, has two meanings. When you're trying to learn a subject that is so complicated, so confusing or so detailed that it seems like it's in another language or from another planet, it's impenetrable — like calculus. Or a physical object can be impenetrable, meaning it is impossible to actually enter or get inside of, like that impenetrable nightclub that has bouncers watching every entrance to keep you and your friends out.
Vocabulary lists containing impenetrable
The Diary of Anne Frank
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The Alchemist
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Tolkien Reading Day, List 1
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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.
The building of the case is well done but what’s most memorable is the impenetrable brick wall of denial constructed by Shirilla’s family and friends in the face of that evidence.
From Los Angeles Times • May 18, 2026
"This missile will make India's security impenetrable and place us among the most powerful nations in the world," it said, without giving further details of the launch.
From Barron's • May 7, 2026
The idea that 5% represents some kind of impenetrable ceiling for yields is misguided, Perz said.
From MarketWatch • May 5, 2026
"I'd be lying if I said I was a completely impenetrable robot," he said.
From BBC • Apr. 10, 2026
Starkey sought to discover this and other lost secrets by careful study of the alchemical texts, which were written, as he acknowledged, in a deliberately impenetrable language.
From "The Invention of Science" by David Wootton
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.
