impenetrable

adjective

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

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 

adverb

Synonyms of impenetrable

• dense
• impervious
• close
• impregnable
• impassable
• impermeable
• thick
• frozen

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

In spite of D'Arcy's best efforts, Rhaenyra is an impenetrable character with illogical choices and zero magnetism to the viewers (or seemingly, her councilors). — Kelly Lawler, USA Today, 21 June 2026

The Shiatsung Project In a bungalow surrounded by an impenetrable wall, a woman has been raised in isolation by a talking screen mounted on the living room wall, fullfilling her every wish without ever revealing the reasons for its life and existence. — Kevin Giraud, Variety, 18 June 2026

For 82 games and three-plus playoff rounds, the bunker remained impenetrable. — Kristian Winfield, New York Daily News, 9 June 2026

Which is okay, because the XLE serves as something of an impenetrable panic room and command center once parked. — New Atlas, 9 June 2026

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