<p><strong>Adjective:</strong></p><ul><li>Having four sides.</li></ul><p><strong>Noun:</strong></p><ul><li>A plane figure having four sides and four angles.</li><li>Something of this form.</li><li>Geometry: a figure formed by four straight lines that have six points of intersection.</li><li>A polygon with four sides.</li><li>The space enclosed between and defended by four fortresses.</li></ul>