| APA | Smart Define. (2015). vertical union thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/vertical_union/thesaurus/narrower |
| Chicago | Smart Define. 2015. "vertical union thesaurus" https://smartdefine.org/vertical_union/thesaurus/narrower (accessed September 21, 2026). |
| Harvard | Smart Define 2015, vertical union thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/vertical_union/thesaurus/narrower>. |
| MLA | Smart Define. "vertical union thesaurus" 13 April 2015. Web. 21 September 2026. <https://smartdefine.org/vertical_union/thesaurus/narrower> |