- (a.) Having four sides, and consequently four angles; quadrangular.
- (n.) An area defended by four fortresses supporting each other; as, the Venetian quadrilateral, comprising Mantua, Peschiera, Verona, and Legnano.
- (n.) A plane figure having four sides, and consequently four angles; a quadrangular figure; any figure formed by four lines.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). quadrilateral. Retrieved September 24, 2026, from http://smartdefine.org/quadrilateral/definitions/2051566 |
| Chicago | Webster's. 2011. "quadrilateral" http://smartdefine.org/quadrilateral/definitions/2051566 (accessed September 24, 2026). |
| Harvard | Webster's 2011, quadrilateral, Smart Define, viewed 24 September, 2026, <http://smartdefine.org/quadrilateral/definitions/2051566>. |
| MLA | Webster's. "quadrilateral" 27 May 2011. Web. 24 September 2026. <http://smartdefine.org/quadrilateral/definitions/2051566> |