| APA | Smart Define. (2013). hard to defeat thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/hard_to_defeat/thesaurus/synonyms |
| Chicago | Smart Define. 2013. "hard to defeat thesaurus" https://smartdefine.org/hard_to_defeat/thesaurus/synonyms (accessed September 21, 2026). |
| Harvard | Smart Define 2013, hard to defeat thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/hard_to_defeat/thesaurus/synonyms>. |
| MLA | Smart Define. "hard to defeat thesaurus" 19 May 2013. Web. 21 September 2026. <https://smartdefine.org/hard_to_defeat/thesaurus/synonyms> |