impenetrable

UK: /ɪmˈpɛnɪtrəb^əl/ US: /ɪmˈpɛnɪtrəbəl/ ,(im pen′i trə bəl)

WordReference Random House Learner's Dictionary of American English © 2025

im•pen•e•tra•ble /ɪmˈpɛnɪtrəbəl/   adj. 

1. that cannot be penetrated:
   an impenetrable barrier.
2. that cannot be understood:
   an impenetrable mystery.

im•pen•e•tra•bil•i•ty /ɪmˌpɛnɪtrəˈbɪlɪti/  n. [uncountable]
im•pen•e•tra•bly, adv.

WordReference Random House Unabridged Dictionary of American English © 2025

im•pen•e•tra•ble  (im pen′i trə bəl), adj. 

1. not penetrable;
   that cannot be penetrated, pierced, entered, etc.
2. inaccessible to ideas, influences, etc.
3. incapable of being understood;
   inscrutable;
   unfathomable:
   an impenetrable mystery.
4. Physics possessing impenetrability.

• Latin impenetrābilis. See im-², penetrable
• late Middle English impenetrabel 1425–75

im•pen′e•tra•ble•ness, n. 
im•pen′e•tra•bly,
adv Synonyms

• 3. incomprehensible, mysterious, obscure, hidden.

Antonyms

• 3. clear, lucid.

Collins Concise English Dictionary © HarperCollins Publishers::

impenetrable / ɪmˈpɛnɪtrəb^əl/ adjective

1. incapable of being pierced through or penetrated: an impenetrable forest
2. incapable of being understood; incomprehensible
3. incapable of being seen through: impenetrable gloom
4. not susceptible to ideas, influence, etc: impenetrable ignorance
5. (of a body) incapable of occupying the same space as another body

imˌpenetraˈbility noun

imˈpenetrableness noun

imˈpenetrably adverb