pentagon

2. The Pentagon is the large five-sided building in the United States where the country's military leaders work.

The reporters waited outside the Pentagon for news.

3. A pentagon can mean any building or room built in the shape of a five-sided figure.

The museum's new hall is a glass pentagon.

4. In geometry, a regular pentagon is a five-sided shape where all sides and angles are equal.

Each angle inside a regular pentagon measures 108 degrees.