| APA | Smart Define. (2013). hardest thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/hardest/thesaurus/synonyms |
| Chicago | Smart Define. 2013. "hardest thesaurus" https://smartdefine.org/hardest/thesaurus/synonyms (accessed September 23, 2026). |
| Harvard | Smart Define 2013, hardest thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/hardest/thesaurus/synonyms>. |
| MLA | Smart Define. "hardest thesaurus" 18 May 2013. Web. 23 September 2026. <https://smartdefine.org/hardest/thesaurus/synonyms> |