| APA | Smart Define. (2015). tough as leather thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/tough_as_leather/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "tough as leather thesaurus" https://smartdefine.org/tough_as_leather/thesaurus/synonyms (accessed September 20, 2026). |
| Harvard | Smart Define 2015, tough as leather thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/tough_as_leather/thesaurus/synonyms>. |
| MLA | Smart Define. "tough as leather thesaurus" 14 April 2015. Web. 20 September 2026. <https://smartdefine.org/tough_as_leather/thesaurus/synonyms> |