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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. 2017.
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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 14, 2009
Historical Examples
  • The little brown girl, with eyes that saw so much and were so impenetrably deep, and the mobile face, so alert and responsive.

    That Fortune Charles Dudley Warner
  • The rushlight had burned out and the cell was impenetrably dark.

    Micah Clarke Arthur Conan Doyle
  • Then there was nothing but the wall itself, dark, thin as a membrane, but impenetrably strong.

    Last Resort Stephen Bartholomew
  • "Till nine o'clock or a little after," suggested Mrs. Travers, impenetrably.

    The Rescue Joseph Conrad
  • The lower front of it seemed to be arched and pillared—and under each arch the shadows were impenetrably black.

    The Seven-Branched Candlestick Gilbert W. (Gilbert Wolf) Gabriel
  • It was a cold, rainy, and impenetrably dark night on the tow-path.

    A Tale of the Tow-Path Homer Greene
  • How had they the craft to find them, so securely, so impenetrably were they hidden!

    The Story of Old Fort Loudon Charles Egbert Craddock
  • The choir is impenetrably dark most of the year at this early hour.

  • Mr. Vanborough looked back into the far corner of the room, in which the lawyer sat, impenetrably waiting for events.

    Man and Wife Wilkie Collins
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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