impenetrable

adjective

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

1

a

: incapable of being penetrated or pierced

b

: inaccessible to knowledge, reason, or sympathy : impervious

2

: incapable of being comprehended : inscrutable

impenetrably

(ˌ)im-ˈpe-nə-trə-blē 

adverb

Synonyms

• impassable
• impassible
• impermeable
• impervious
• impregnable

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

Studying Trump’s image-making is, for better or worse, one of the few windows into the worldview of an otherwise impenetrable figure. —Leah Dolan, CNN, 18 Jan. 2025

Special run-flat tires, a new thing at the time, finish off the impenetrable visage. —Josh Max, Forbes, 17 Jan. 2025

Although part of the Thai mainland, Railay Beach is sometimes mistaken for an island because it’s cut off from its surroundings by impenetrable karst limestone cliffs and dense mangrove forests. —Nicholas Derenzo, AFAR Media, 13 Jan. 2025

Just as Lewis’s beloved book found humanity in seemingly impenetrable data, so too does Chris Mark’s lifelong quest become as riveting as a rescue mission. —Longreads, 18 Dec. 2024

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

Kids Definition

impenetrable

adjective

im·​pen·​e·​tra·​ble (ˈ)im-ˈpen-ə-trə-bəl 

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 

adverb