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

---

impregnable ² British  

/ ˌɪmprɛɡˈneɪtəbəl, ɪmˈprɛɡnəbəl /

adjective

1. able to be impregnated; fertile

---

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

Though the Cuban government has acknowledged talks, Díaz-Canel warned last month that “any act of aggression will clash with an impregnable resistance.”

From The Wall Street Journal • Apr. 3, 2026

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

“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

The great clipper, so seemingly impregnable, had become impossibly small.

From "Ship Breaker" by Paolo Bacigalupi

Related Words

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