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# Definition of: quadrilateral

(kwod′rə·lat**′**ər·əl) adjective

Formed or bounded by four lines; four-sided.

—*noun* **1.** Geom. **a** A figure bounded by four straight lines terminated at four angles. **b** A figure formed of four infinite straight lines, having six intersections. **2.** A space or area defended by four enclosing fortresses. [<L *quadrilaterus* <*quattuor* four + *latus, lateris* side]

QUADRILATERAL*abdc.* Quadrilateral.*ad., bc.* Diagonals.*ebfc.* Quadrilateral.*a., b., c., d., f.* Vertices.*ai., bh., ei.* Diagonals.*g., hh., i.* Centers.