| APA | Smart Define. (2013). thermionic valve thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/thermionic_valve/thesaurus/narrower |
| Chicago | Smart Define. 2013. "thermionic valve thesaurus" https://smartdefine.org/thermionic_valve/thesaurus/narrower (accessed September 22, 2026). |
| Harvard | Smart Define 2013, thermionic valve thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/thermionic_valve/thesaurus/narrower>. |
| MLA | Smart Define. "thermionic valve thesaurus" 19 May 2013. Web. 22 September 2026. <https://smartdefine.org/thermionic_valve/thesaurus/narrower> |