- (a.) Having the property of preventing any other substance from occupying the same space at the same time.
- (a.) Inaccessible, as to knowledge, reason, sympathy, etc.; unimpressible; not to be moved by arguments or motives; as, an impenetrable mind or heart.
- (a.) Incapable of being penetrated or pierced; not admitting the passage of other bodies; not to be entered; impervious; as, an impenetrable shield.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). impenetrable. Retrieved September 23, 2026, from http://smartdefine.org/impenetrable/definitions/2019481 |
| Chicago | Webster's. 2011. "impenetrable" http://smartdefine.org/impenetrable/definitions/2019481 (accessed September 23, 2026). |
| Harvard | Webster's 2011, impenetrable, Smart Define, viewed 23 September, 2026, <http://smartdefine.org/impenetrable/definitions/2019481>. |
| MLA | Webster's. "impenetrable" 27 May 2011. Web. 23 September 2026. <http://smartdefine.org/impenetrable/definitions/2019481> |