| APA | Smart Define. (2013). to harden thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/to_harden/thesaurus/synonyms |
| Chicago | Smart Define. 2013. "to harden thesaurus" https://smartdefine.org/to_harden/thesaurus/synonyms (accessed September 26, 2026). |
| Harvard | Smart Define 2013, to harden thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/to_harden/thesaurus/synonyms>. |
| MLA | Smart Define. "to harden thesaurus" 18 May 2013. Web. 26 September 2026. <https://smartdefine.org/to_harden/thesaurus/synonyms> |