Definition of Quadrilateral

having four sides. | A polygon with four sides. | An area defended by four fortresses supporting each other.

- It crystallizes in small
**quadrilateral**prisms, white and transparent, or in needles grouped in stars. - Three more of the steel spikes were hammered into the surface, forming a rough
**quadrilateral**around the Pole. - In the southeast you will recognize the
**quadrilateral**of Corvus, with the remarkably white star Spica glittering east of it. - The three pairs of rays which may be drawn from a point through the three pairs of opposite vertices of a complete
**quadrilateral**are said to be in involution. - The four lines joining the two opposite pairs of vertices and the two opposite points of contact of a
**quadrilateral**circumscribed about a conic all meet in a point. - Given a simple
**quadrilateral**inscribed in a conic section, every transversal meets the conic and the four sides of the**quadrilateral**in six points which are in involution. - The turning of the Quadrilateral meant the adoption of a route into Venetia across the Po below Mantua.
- If a
**quadrilateral**be inscribed in a conic, two pairs of opposite sides and the tangents at opposite vertices intersect in four points, all of which lie on a straight line. - If a
**quadrilateral**be circumscribed about a conic, the lines joining two pairs of opposite vertices and the lines joining two opposite points of contact are four lines which meet in a point.