| APA | Smart Define. (2016). sullen thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/sullen/thesaurus/antonyms |
| Chicago | Smart Define. 2016. "sullen thesaurus" https://smartdefine.org/sullen/thesaurus/antonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2016, sullen thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/sullen/thesaurus/antonyms>. |
| MLA | Smart Define. "sullen thesaurus" 24 March 2016. Web. 25 September 2026. <https://smartdefine.org/sullen/thesaurus/antonyms> |