Source : Webster's Revised Unabridged Dictionary (1913)

Quadrilateral \Quad`ri*lat"er*al\, a. [L. quadrilaterus: cf. F.
   quadrilat[`e]re, quadrilat['e]ral. See {Quadri-} and
   {Lateral}.]
   Having four sides, and consequently four angles;
   quadrangular.

Quadrilateral \Quad`ri*lat"er*al\, n.
   1. (Geom.) 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} (Geom.), 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 : WordNet®

quadrilateral
     adj : having four sides [syn: {four-sided}]
     n : a four-sided polygon [syn: {quadrangle}, {tetragon}]