| APA | Smart Define. (2013). impenetrably thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/impenetrably/thesaurus/synonyms |
| Chicago | Smart Define. 2013. "impenetrably thesaurus" https://smartdefine.org/impenetrably/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2013, impenetrably thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/impenetrably/thesaurus/synonyms>. |
| MLA | Smart Define. "impenetrably thesaurus" 17 June 2013. Web. 25 September 2026. <https://smartdefine.org/impenetrably/thesaurus/synonyms> |