Pentagon (noun)

1. A polygon with five sides and five angles.
2. The building in Washington, D.C., that serves as the headquarters of the United States Department of Defense and as the meeting place for the National Security Council.

Origin:

From late latin pentagonum, from greek pente (five) + gōnia (angle), from gōnía (corner).

Examples:

1. A pentagon has five sides and five angles.
2. The Pentagon is the headquarters of the United States Department of Defense.
3. The Pentagon is the largest office building in the world.
4. The pentagon shape is often used in military symbols and logos.
5. The pentagon is a regular polygon, meaning all of its sides and angles are congruent.