| APA | Smart Define. (2016). red-letter day thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/red-letter_day/thesaurus/narrower |
| Chicago | Smart Define. 2016. "red-letter day thesaurus" https://smartdefine.org/red-letter_day/thesaurus/narrower (accessed September 28, 2026). |
| Harvard | Smart Define 2016, red-letter day thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/red-letter_day/thesaurus/narrower>. |
| MLA | Smart Define. "red-letter day thesaurus" 29 February 2016. Web. 28 September 2026. <https://smartdefine.org/red-letter_day/thesaurus/narrower> |