im·​pen·​e·​tra·​ble | \(ˌ)im-ˈpe-nə-trə-bəl \

Definition of impenetrable 

1a : incapable of being penetrated or pierced

b : inaccessible to knowledge, reason, or sympathy : impervious

2 : incapable of being comprehended : inscrutable

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Other Words from impenetrable

impenetrably \(ˌ)im-​ˈpe-​nə-​trə-​blē \ adverb

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

Pondering the impenetrable fog of the early universe. Lacy Schley, Discover Magazine, "Staring Into the Abyss," 24 Nov. 2018 He is protected by an impenetrable and ever-present armor of enthusiasm that has helped him endure any setback, letdown or underestimation. Kayleigh Roberts, Marie Claire, "Taylor Swift (Kind of) Came Out of Hiding to Praise BFF Ed Sheeran," 20 Apr. 2017 The two sit in awkward silence, separated by their gaping age difference and by an impenetrable language barrier (the old man’s dialogue is even scribbled in Thai). John Lithgow, New York Times, "Grandmas and Grandpas Are a Kid’s Natural Allies in These Books," 22 June 2018 Early in the episode, Bernard and Elsie have an impenetrable conversation about the Cradle and the Mesa—two key aspects of Westworld’s behind-the-scenes power structure, which are each vying for control in the wake of the revolution. Scott Meslow, GQ, "Westworld Season 2 Episode 6 Recap: Off the Rails," 28 May 2018 Donald Trump's electoral coalition is smashing both American political parties and its previously impenetrable political news media. Fox News, "'The Great Revolt' by Salena Zito and Brad Todd," 8 May 2018 But as drive-ins started to multiply in the suburbs — there were at least 37 in the Bay Area by the 1960s — San Francisco was an impenetrable market. Peter Hartlaub,, "SF almost had a Sutro Drive-In in 1950, and more local outdoor movie history," 13 July 2018 Coal dust particles enter the lungs, irritating the delicate lung tissue and eventually forming massive impenetrable fibrous tissue that significantly restricts the lung's functions and causes scarring, which can lead to lung failure and death. Beth Warren, The Courier-Journal, "Kentucky coal mine officials charged with cheating on key safety tests," 11 July 2018 Genuine, unanswered and impenetrable mysteries are rare in modern football: rare, in fact, in modern life., "Ronaldo's 1998 Seizure & World Cup Final Appearance Remains One of Football's Greatest Mysteries," 1 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'impenetrable.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of impenetrable

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

History and Etymology for impenetrable

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

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Last Updated

13 Dec 2018

Look-up Popularity

Time Traveler for impenetrable

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

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More Definitions for impenetrable



English Language Learners Definition of impenetrable

: impossible to pass or see through

: impossible to understand


im·​pen·​e·​tra·​ble | \im-ˈpe-nə-trə-bəl \

Kids Definition of impenetrable

1 : impossible to pass through or see through impenetrable walls impenetrable darkness

2 : impossible to understand an impenetrable mystery

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Comments on impenetrable

What made you want to look up impenetrable? Please tell us where you read or heard it (including the quote, if possible).


living or existing for a long time

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