| APA | Smart Define. (2011). twenty-first century thesaurus. Retrieved September 30, 2026, from https://smartdefine.org/twenty-first_century/thesaurus/antonyms |
| Chicago | Smart Define. 2011. "twenty-first century thesaurus" https://smartdefine.org/twenty-first_century/thesaurus/antonyms (accessed September 30, 2026). |
| Harvard | Smart Define 2011, twenty-first century thesaurus, Smart Define, viewed 30 September, 2026, <https://smartdefine.org/twenty-first_century/thesaurus/antonyms>. |
| MLA | Smart Define. "twenty-first century thesaurus" 24 May 2011. Web. 30 September 2026. <https://smartdefine.org/twenty-first_century/thesaurus/antonyms> |