| APA | Smart Define. (2015). difficultness thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/difficultness/thesaurus/narrower |
| Chicago | Smart Define. 2015. "difficultness thesaurus" https://smartdefine.org/difficultness/thesaurus/narrower (accessed September 20, 2026). |
| Harvard | Smart Define 2015, difficultness thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/difficultness/thesaurus/narrower>. |
| MLA | Smart Define. "difficultness thesaurus" 10 April 2015. Web. 20 September 2026. <https://smartdefine.org/difficultness/thesaurus/narrower> |