| APA | Smart Define. (2015). toughen thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/toughen/thesaurus/narrower |
| Chicago | Smart Define. 2015. "toughen thesaurus" https://smartdefine.org/toughen/thesaurus/narrower (accessed September 24, 2026). |
| Harvard | Smart Define 2015, toughen thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/toughen/thesaurus/narrower>. |
| MLA | Smart Define. "toughen thesaurus" 13 April 2015. Web. 24 September 2026. <https://smartdefine.org/toughen/thesaurus/narrower> |