1. a flat shape with five straight sides and five angles
Usage: geometry
2. the Pentagon: the headquarters of the U.S. Department of Defense
Usage: proper noun

Examples

• The students learned to draw a pentagon in geometry class.
• A regular pentagon has all sides of equal length.
• The building was designed in the shape of a pentagon.
• The Pentagon announced new military policies today.
• She works at the Pentagon as a defense analyst.
• The Pentagon’s five-sided structure is iconic in Washington, D.C.