- not penetrable; that cannot be penetrated, pierced, entered, etc.
- inaccessible to ideas, influences, etc.
- incapable of being understood; inscrutable; unfathomable: an impenetrable mystery.
- possessing impenetrability.
- incapable of being pierced through or penetrated
- incapable of being understood; incomprehensible
- incapable of being seen through
- not susceptible to ideas, influence, etc
- (of a body) incapable of occupying the same space as another body
