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[im-pen-i-truh-buh l] /ɪmˈpɛn ɪ trə bəl/
not penetrable; that cannot be penetrated, pierced, entered, etc.
inaccessible to ideas, influences, etc.
incapable of being understood; inscrutable; unfathomable:
an impenetrable mystery.
Physics. possessing impenetrability.
Origin of impenetrable
late Middle English
1425-75; late Middle English impenetrabel < Latin impenetrābilis. See im-2, penetrable
Related forms
impenetrableness, noun
impenetrably, adverb
3. incomprehensible, mysterious, obscure, hidden.
3. clear, lucid. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for impenetrably
Contemporary Examples
  • “In this country that we were told was impenetrably dangerous, guys were just turning up,” he said.

    Iraq, Under the Boot Jace Lacob October 15, 2009
Historical Examples
  • The rushlight had burned out and the cell was impenetrably dark.

    Micah Clarke Arthur Conan Doyle
  • "Till nine o'clock or a little after," suggested Mrs. Travers, impenetrably.

    The Rescue Joseph Conrad
  • But Wilkins was as impenetrably suave as he had been the day before.

    The Search Party G. A. Birmingham
  • It was a cold, rainy, and impenetrably dark night on the tow-path.

    A Tale of the Tow-Path Homer Greene
  • The choir is impenetrably dark most of the year at this early hour.

  • All through this sitting the brothers had been impenetrably guarded.

  • How had they the craft to find them, so securely, so impenetrably were they hidden!

    The Story of Old Fort Loudon Charles Egbert Craddock
  • He took no notice of my interruption; he went on impenetrably with his calculations.

    The Law and the Lady Wilkie Collins
  • It was ten feet high, and its interior was impenetrably black.

    A Voyage to Arcturus David Lindsay
British Dictionary definitions for impenetrably


incapable of being pierced through or penetrated: an impenetrable forest
incapable of being understood; incomprehensible: impenetrable jargon
incapable of being seen through: impenetrable gloom
not susceptible to ideas, influence, etc: impenetrable ignorance
(physics) (of a body) incapable of occupying the same space as another body
Derived Forms
impenetrability, noun
impenetrableness, noun
impenetrably, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for impenetrably



mid-15c., from Middle French impenetrable, from Latin impenetrabilis "that cannot be penetrated," from assimilated form of in- "not, opposite of" (see in- (1)) + penetrabilis "penetrable" (see penetrate). Related: Impenetrably; impenetrability.

Online Etymology Dictionary, © 2010 Douglas Harper
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