- not penetrable; that cannot be penetrated, pierced, entered, etc.
- inaccessible to ideas, influences, etc.
- incapable of being understood; inscrutable; unfathomable: an impenetrable mystery.
- Physics. possessing impenetrability.
- incapable of being pierced through or penetratedan impenetrable forest
- incapable of being understood; incomprehensibleimpenetrable jargon
- incapable of being seen throughimpenetrable gloom
- not susceptible to ideas, influence, etcimpenetrable ignorance
- physics (of a body) incapable of occupying the same space as another body
mid-15c., from Middle French impenetrable, from Latin impenetrabilis “that cannot be penetrated,” from assimilated form of in- “not, opposite of” (see in- (1)) + penetrabilis “penetrable” (see penetrate). Related: Impenetrably; impenetrability.