quadrilateral

a.

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

n.

  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.