pentagon

American  

[pen-tuh-gon, -guhn] / ˈpɛn təˌgɒn, -gən /

noun

1. a polygon having five angles and five sides.

2. the Pentagon,

   1. a building in Arlington, Virginia, having a plan in the form of a regular pentagon, containing most U.S. Defense Department offices.

   2. the U.S. Department of Defense; the U.S. military establishment.

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pentagon ¹ British  

/ ˈpɛntəˌɡɒn, pɛnˈtæɡənəl /

noun

1. a polygon having five sides

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Pentagon ² British  

/ ˈpɛntəˌɡɒn /

noun

1. the five-sided building in Arlington, Virginia, that houses the headquarters of the US Department of Defense

2. the military leadership of the US

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pentagon Scientific  

/ pĕn′tə-gŏn′ /

1. A polygon having five sides.

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Pentagon ¹ Cultural  

1. An immense five-sided building in Virginia, just outside Washington, D.C., that serves as headquarters for the Department of Defense.

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pentagon ² Cultural  

1. A polygon having five sides.

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Discover More

The term is often used to refer to the Department of Defense or the military: “The Pentagon agreed today to submit the modified weapons plan to the president.”

The Pentagon was severely damaged by the September 11 attacks.

The Pentagon is a huge five-sided building near Washington, D.C., that contains offices of the Department of Defense.

Other Word Forms

• pentagonal adjective
• pentagonally adverb
• subpentagonal adjective

Etymology

Origin of pentagon

1560–70; < Late Latin pentagōnum < Greek pentágōnon, noun use of neuter of pentágōnos five-angled. See penta-, -gon

Explanation

A pentagon is a five-sided polygon: it has one more side than a square. This is a word you're most likely to learn in math class when studying geometry: a pentagon is a polygon that has five sides. There are many words for shapes that indicate their specific number of sides, such as octagon: a polygon with eight sides. The root penta means "five," which is why a pentagram has five points. You may have heard of the Pentagon, which is the center of the U.S. military in Washington D.C. It has this name because the building has five sides.

Example Sentences

Hint: It’s what you get when you subtract a twogon from a pentagon.

From Slate • Feb. 22, 2025

The vision involves developing human capital, the digital economy and inclusivity and sustainability, he said, referring to it as the "pentagon strategy".

From Reuters • Sep. 4, 2023

They could arrange four hat tiles into a hexagonlike structure, two tiles into a pentagon and another combination of two tiles into a parallelogram.

From Scientific American • Apr. 10, 2023

Thin striped legs extend from each point of the pentagon.

From Textbooks • Jan. 1, 2015

Nestled within the lines of the star is a pentagon.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife