| APA | Smart Define. (2015). vacuum tube thesaurus. Retrieved September 29, 2026, from https://smartdefine.org/vacuum_tube/thesaurus/narrower |
| Chicago | Smart Define. 2015. "vacuum tube thesaurus" https://smartdefine.org/vacuum_tube/thesaurus/narrower (accessed September 29, 2026). |
| Harvard | Smart Define 2015, vacuum tube thesaurus, Smart Define, viewed 29 September, 2026, <https://smartdefine.org/vacuum_tube/thesaurus/narrower>. |
| MLA | Smart Define. "vacuum tube thesaurus" 10 April 2015. Web. 29 September 2026. <https://smartdefine.org/vacuum_tube/thesaurus/narrower> |