impenetrable

adjective

im·​pen·​e·​tra·​ble (ˌ)im-ˈpe-nə-trə-bəl How to pronounce impenetrable (audio)
Synonyms of impenetrable
1
a
: incapable of being penetrated or pierced
impenetrable armor
b
: inaccessible to knowledge, reason, or sympathy : impervious
an impenetrable heart
2
: incapable of being comprehended : inscrutable
an impenetrable mystery
impenetrably
(ˌ)im-ˈpe-nə-trə-blē How to pronounce impenetrable (audio)
adverb

Synonyms of impenetrable

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Examples of impenetrable in a Sentence

The fort's defenses were thought to be impenetrable. the ancient temple was surrounded by vast stretches of impenetrable jungle
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Child safety experts lauded the settlement and the accompanying pressure campaign as a giant leap forward in the effort to regulate an industry that until this year appeared all but impenetrable to reform, either from the courts or legislatures. — Sonja Sharp, Los Angeles Times, 29 Aug. 2026 The space offers guests a rare glimpse into a facet of Japanese nightlife that can feel impenetrable to outsiders. — Condé Nast, Condé Nast Traveler, 26 Aug. 2026 Chalk it up to the leftover hubris of late-20th-century American empire and the grand illusion of a liberated civilization thriving behind an impenetrable fortress. — Andy Andersen, Vulture, 16 Aug. 2026 The rule also failed to tackle all of the ways trusts and other vehicles provide impenetrable secrecy for the wealthy and the crooked alike. — Casey Michel, The Atlantic, 14 Aug. 2026 See All Example Sentences for impenetrable

Word History

Etymology

Middle English impenetrabel, from Middle French impenetrable, from Latin impenetrabilis, from in- + penetrabilis penetrable

First Known Use

15th century, in the meaning defined at sense 1a

Time Traveler
The first known use of impenetrable was in the 15th century

Rhymes for impenetrable

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Browse Nearby Words

impenetrability
impenetrable
impenetrate
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Cite this Entry

“Impenetrable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/impenetrable. Accessed 1 Sep. 2026.

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Kids Definition

impenetrable

adjective
im·​pen·​e·​tra·​ble (ˈ)im-ˈpen-ə-trə-bəl How to pronounce impenetrable (audio)
1
: impossible to get through or into
impenetrable walls
impenetrable jungle
2
: impossible to understand
an impenetrable mystery
impenetrability
(ˌ)im-ˌpen-ə-trə-ˈbil-ət-ē
noun
impenetrably
(ˈ)im-ˈpen-ə-trə-blē How to pronounce impenetrable (audio)
adverb
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