The origin of the word `quadrilateral` is the two Latin words quadri, a variant of four, and latus, meaning `side`. Quadrilaterals are simple (not self-intersecting) or complex (self-intersecting), also called crossed. Simple quadrilaterals are either convex or concave. This is a special case of the n-gon interior angle sum formula (n − 2)

(from the article `Christianity`) ...apostolic principles.` Among Episcopalians, the visionaries for unity included Thomas Hubbard Vail, William Augustus Muhlenberg, and William Reed ...
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(kwod″rĭ-lat´әr-әl) having four sides. a four-sided figure.
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[adj] - having four sides 2. [n] - a four-sided polygon

• (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 f...

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1. <geometry> 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. ... <geometry> Complete quadrilateral, the figure made ...
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A cell near the base of the damselfly wing, whose shape is important in separating the families.
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a four-sided polygon
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A polygon that has four sides and four vertices (corners). Quadrilaterals, and polygons in general, may be convex or concave. A convex quadrilateral may be further classified as a trapezoid or a British trapezium (one pair of opposite sides are parallel), a trapezium (no sides parallel); an isoscele...

A polygon with four sides
Examples:

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A quadrilateral is a four-sided polygon.
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famous combination of four fortresses mutually supporting one another, during the Austrian rule of northern Italy. The four fortified towns were ...
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four-sided
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