• synonyms


  1. not penetrable; that cannot be penetrated, pierced, entered, etc.
  2. inaccessible to ideas, influences, etc.
  3. incapable of being understood; inscrutable; unfathomable: an impenetrable mystery.
  4. Physics. possessing impenetrability.
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Origin of impenetrable

1425–75; late Middle English impenetrabel < Latin impenetrābilis. See im-2, penetrable
Related formsim·pen·e·tra·ble·ness, nounim·pen·e·tra·bly, adverb



Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for impenetrably

Contemporary Examples

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.

  • The choir is impenetrably dark most of the year at this early hour.

British Dictionary definitions for impenetrably


  1. incapable of being pierced through or penetratedan impenetrable forest
  2. incapable of being understood; incomprehensibleimpenetrable jargon
  3. incapable of being seen throughimpenetrable gloom
  4. not susceptible to ideas, influence, etcimpenetrable ignorance
  5. physics (of a body) incapable of occupying the same space as another body
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Derived Formsimpenetrability, nounimpenetrableness, nounimpenetrably, 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

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.

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Online Etymology Dictionary, © 2010 Douglas Harper