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

Artificial intelligence is even peering through the most impenetrable of artifacts: ancient, charred scrolls that are too delicate to be unfurled. —Ashley Strickland, CNN, 8 Feb. 2025

What may sound conceptually impenetrable again proves to function not only well, but with humanity, with the release of Horsegiirl’s debut EP, v.i.p. – very important pony. —Katie Bain, Billboard, 24 Jan. 2025

This may seem like an impossible task in a world where politics is becoming more divisive, foreign policy more parochial, and social media bubbles more impenetrable. —Harvey Whitehouse, WIRED, 23 Jan. 2025

In fact, the dust in the disk is so impenetrable that T Tauri South A and B are only visible in infrared light, which can pass through the dust relatively unattenuated. —Keith Cooper, Space.com, 23 Jan. 2025

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