Definition of: impenetrable

(im·pen′ə·trə·bəl) adjective
1. That cannot be penetrated or pierced: said of material things.
2. That cannot be penetrated by the eye or mind; abstruse; dense: an impenetrable darkness or mystery.
3. Not to be affected by moral considerations: an impenetrable conscience.
4. Possessing the property of impenetrability. [<OF impenetrable <L impenetrabilis]
—im·pen′e·tra·bly adverb Synonyms: close, dense, hard, impassable, impermeable, impervious, solid. See HARD. Antonyms: fluid, loose, open, penetrable, pervious, soft, yielding.