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

Cybersecurity strategy has undergone a fundamental shift—from aspiring to build impenetrable defenses to accepting that breaches are inevitable. —Tony Bradley, Forbes.com, 15 May 2025

But in person, nothing about her seems impenetrable. —Thania Garcia, Variety, 9 May 2025

Like those two men, Combs' power and influence created an impenetrable cocoon of privilege that, prosecutors will argue, insulated him from repercussions while devastating the lives of men and women who stayed largely silent for fear of his reach. —Marco Della Cava, USA Today, 6 May 2025

That impenetrable wall made Jackson feel safe, and it got broken. —Katie Campione, Deadline, 20 Apr. 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

Rhymes for impenetrable

• penetrable

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