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Synonyms

impregnable

1 American  
[im-preg-nuh-buhl] / ɪmˈprɛg nə bəl /

adjective

  1. strong enough to resist or withstand attack; not to be taken by force, unconquerable.

    an impregnable fort.
    Synonyms:
    invulnerable
    Antonyms:
    vulnerable

  2. not to be overcome or overthrown.

    an impregnable argument.
    Synonyms:
    unassailable
impregnable 2 American  
[im-preg-nuh-buhl] / ɪmˈprɛg nə bəl /

adjective

  1. susceptible to impregnation, as an egg.

impregnable 1 British  
/ ɪmˈprɛɡnəbəl /

adjective

  1. unable to be broken into or taken by force

    an impregnable castle

  2. unable to be shaken or overcome

    impregnable self-confidence

  3. incapable of being refuted

    an impregnable argument
"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
impregnable 2 British  
/ ˌɪmprɛɡˈneɪtəbəl, ɪmˈprɛɡnəbəl /

adjective

  1. able to be impregnated; fertile

"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

Related Words

See invincible.

Other Word Forms

  • impregnability noun
  • impregnableness noun
  • impregnably adverb

Etymology

Origin of impregnable1

First recorded in 1400–50; late Middle English impregnable, imprenable, from Middle French, equivalent to im- im- 2 + prenable pregnable

Origin of impregnable2

impregn(ate) + -able

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.

That had seemed like an impregnable advantage for S&P Global.

From The Wall Street Journal • Feb. 4, 2026

“Some criminals have understood that museums are not impregnable cultural fortresses,” said Pierre Noual, a French lawyer specializing in cultural heritage law.

From The Wall Street Journal • Nov. 13, 2025

“It’s like hitting a bullet with a bullet,” someone says, crushing the naive notion of an impregnable “nuclear defense.”

From Los Angeles Times • Oct. 9, 2025

Their 416 in the first innings was a good total, though their wastefulness prevented it from being impregnable.

From BBC • Jul. 19, 2024

"The Eyrie is impregnable," Lysa Arryn declared calmly.

From "A Game of Thrones" by George R.R. Martin

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.