| APA | Smart Define. (2013). periodic event thesaurus. Retrieved September 27, 2026, from https://smartdefine.org/periodic_event/thesaurus/narrower |
| Chicago | Smart Define. 2013. "periodic event thesaurus" https://smartdefine.org/periodic_event/thesaurus/narrower (accessed September 27, 2026). |
| Harvard | Smart Define 2013, periodic event thesaurus, Smart Define, viewed 27 September, 2026, <https://smartdefine.org/periodic_event/thesaurus/narrower>. |
| MLA | Smart Define. "periodic event thesaurus" 18 May 2013. Web. 27 September 2026. <https://smartdefine.org/periodic_event/thesaurus/narrower> |