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

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

Synonyms for impenetrable

Antonyms for impenetrable Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for impenetrable

Contemporary Examples of impenetrable

Historical Examples of impenetrable

  • “An impenetrable mystery” was sure “to hang for ever” as far as all mankind was concerned.

    The Secret Agent

    Joseph Conrad

  • Kirkwood smiled grimly, with a face of brass, impenetrable, inflexible.

    The Black Bag

    Louis Joseph Vance

  • Go not to the Alhambra: the fort is impenetrable—the guard faithful.

    Leila, Complete

    Edward Bulwer-Lytton

  • He had been prepared for abuse, but not for impenetrable silence.

  • Since then Tawabinisy had hidden himself behind his impenetrable grin.

    The Forest

    Stewart Edward White

British Dictionary definitions for impenetrable



incapable of being pierced through or penetratedan impenetrable forest
incapable of being understood; incomprehensibleimpenetrable jargon
incapable of being seen throughimpenetrable gloom
not susceptible to ideas, influence, etcimpenetrable ignorance
physics (of a body) incapable of occupying the same space as another body
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 impenetrable

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