| APA | Smart Define. (2015). sullen expression thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/sullen_expression/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "sullen expression thesaurus" https://smartdefine.org/sullen_expression/thesaurus/synonyms (accessed September 23, 2026). |
| Harvard | Smart Define 2015, sullen expression thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/sullen_expression/thesaurus/synonyms>. |
| MLA | Smart Define. "sullen expression thesaurus" 10 April 2015. Web. 23 September 2026. <https://smartdefine.org/sullen_expression/thesaurus/synonyms> |