| APA | Smart Define. (2013). impenetrably thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/impenetrably/thesaurus/antonyms |
| Chicago | Smart Define. 2013. "impenetrably thesaurus" https://smartdefine.org/impenetrably/thesaurus/antonyms (accessed September 26, 2026). |
| Harvard | Smart Define 2013, impenetrably thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/impenetrably/thesaurus/antonyms>. |
| MLA | Smart Define. "impenetrably thesaurus" 17 June 2013. Web. 26 September 2026. <https://smartdefine.org/impenetrably/thesaurus/antonyms> |