1. Noun. A four-sided polygon.

Generic synonyms: Polygon, Polygonal Shape
Specialized synonyms: Parallelogram, Trapezium, Trapezoid

Exact synonyms: Four-sided
Similar to: Many-sided, Multilateral

1. a. Having four sides, and consequently four angles; quadrangular.

2. n. A plane figure having four sides, and consequently four angles; a quadrangular figure; any figure formed by four lines.

1. Noun. a polygon having four sides. ¹

2. Adjective. having four sides. ¹

¹ Source: wiktionary.com

1. [n -S]

1. 1. A plane figure having four sides, and consequently four angles; a quadrangular figure; any figure formed by four lines. 2. An area defended by four fortresses supporting each other; as, the Venetian quadrilateral, comprising Mantua, Peschiera, Verona, and Legnano. Complete quadrilateral, the figure made up of the six straight lines that can be drawn through four points, A, B, C, I, the lines being supposed to be produced indefinitely. Source: Websters Dictionary (01 Mar 1998)

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Below you will find example usage of this term as found in modern and/or classical literature:

1. Projective Geometry by Oswald Veblen, John Wesley Young (1910)
"It consists of four quadrilateral. It consists of four vertices and six sides. ... quadrilateral.* The assumptions A and E on which all our reasoning is ..."

2. The Advanced Part of A Treatise on the Dynamics of a System of Rigid Bodies by Edward John Routh (1892)
"Network with quadrilateral openings. To bring these particles into order we ... Show that the geometrical peculiarity of this quadrilateral network is that ..."

3. The Advanced Part of A Treatise on the Dynamics of a System of Rigid Bodies by Edward John Routh (1892)
"Network with quadrilateral openings. To bring these particles into order we ... Show that the geometrical peculiarity of this quadrilateral network is that ..."

4. Trilinear Coordinates and Other Methods of Modern Analytical Geometry of Two by William Allen Whitworth (1866)
"So the critical circumscribed conic of the quadrilateral CAC'A ' touches the four straight lines Cc, Aa, C'c, A'a, and the critical circumscribed conic of ..."

5. The Theory and Practice of Surveying: Designed for the Use of Surveyors and by John Butler Johnson (1886)
"In the quadrilateral in Fig. 142 there are eight observed angles, A,, ... In the quadrilateral ABCD we have four triangles in which all the angles have been ..."

6. Trilinear Coordinates and Other Methods of Modern Analytical Geometry of Two by William Allen Whitworth (1866)
"So the critical circumscribed conic of the quadrilateral CAC'A' touches the ... Amongst the conies inscribed in the quadrilateral BCBC' there is one whose ..."