| APA | Smart Define. (2015). pen in thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/pen_in/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "pen in thesaurus" https://smartdefine.org/pen_in/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2015, pen in thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/pen_in/thesaurus/synonyms>. |
| MLA | Smart Define. "pen in thesaurus" 10 April 2015. Web. 25 September 2026. <https://smartdefine.org/pen_in/thesaurus/synonyms> |