Definition of quadrilateral

What does the word quadrilateral mean?

• part of speech: noun

  [L.] A name applied to countries forming a sort of square, guarded by four fortresses, as the Q. of Peschiera, Verona, Legnano, and Mantua.

• part of speech: noun

  [L.] Geom.) A plane figure bounded by four straight lines. If no two sides are parallel, it is a Trapezium; if it has only one pair of sides parallel, it is a Trapezoid; if it has two pairs of parallel sides, a Parallelogram, which is a rectangle or oblong when its angles are right angles, and a square if the four sides are equal and the angles right angles; if the four sides are equal but the angles not right angles, it is a Rhombus. See Rhomboid.