| APA | Smart Define. (2015). past perfect thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/past_perfect/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "past perfect thesaurus" https://smartdefine.org/past_perfect/thesaurus/synonyms (accessed September 20, 2026). |
| Harvard | Smart Define 2015, past perfect thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/past_perfect/thesaurus/synonyms>. |
| MLA | Smart Define. "past perfect thesaurus" 10 April 2015. Web. 20 September 2026. <https://smartdefine.org/past_perfect/thesaurus/synonyms> |