| APA | Smart Define. (2013). letter-box thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/letter-box/thesaurus/synonyms |
| Chicago | Smart Define. 2013. "letter-box thesaurus" https://smartdefine.org/letter-box/thesaurus/synonyms (accessed September 21, 2026). |
| Harvard | Smart Define 2013, letter-box thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/letter-box/thesaurus/synonyms>. |
| MLA | Smart Define. "letter-box thesaurus" 18 May 2013. Web. 21 September 2026. <https://smartdefine.org/letter-box/thesaurus/synonyms> |