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

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impregnable ² American  

[im-preg-nuh-buhl] / ɪmˈprɛg nə bəl /

adjective

1. susceptible to impregnation, as an egg.

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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

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impregnable ² British  

/ ˌɪmprɛɡˈneɪtəbəl, ɪmˈprɛɡnəbəl /

adjective

1. able to be impregnated; fertile

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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

Explanation

When something is impregnable it is not easily taken by force and can stand up to any attack. We usually use it in reference to some form of protection, like a fort or a solid defensive line in football. The genealogy of the adjective impregnable includes the Middle French word prenable, meaning "vulnerable, easily conquered," which itself came from the verb prendre, which meant "to take." The addition of the negative prefix im- flipped the meaning. Impregnable can be used to describe anything that cannot be entered or successfully attacked. Seventeenth-century theater critic Jeremy Collier once said, "True courage is a result of reasoning. A brave mind is always impregnable."

Example Sentences

Infantino has clashed with players' unions and European football, but he remains in an impregnable position at the top of the world game.

From BBC • Feb. 25, 2026

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

From The Wall Street Journal • Feb. 4, 2026

Singapore was considered impregnable, but it wasn’t prepared for an attack from the mainland, and its 60,000-strong garrison surrendered on Feb. 8, 1942, the worst defeat in British history.

From The Wall Street Journal • Oct. 27, 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

They could lay bare in the utmost detail everything that you had done or said or thought; but the inner heart, whose workings were mysterious even to yourself, remained impregnable.

From "1984" by George Orwell

Related Words

• fortified
• impenetrable
• indestructible
• invincible
• invulnerable
• unassailable