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• pentagon
  pentagon

  noun

  a polygon having five angles and five sides.
• Pentagon
  Pentagon

  noun

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

pentagon

American  

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

noun

• pentagons
  plural

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 /

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

Derived Forms

• pentagonal
  adjective
• subpentagonal
  adjective
• pentagonally
  adverb

Inflected Forms

Nouns

• pentagons
  plural

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

See Examples For:

pentagon Pentagon pentagons

The capital-P version outside Washington, D.C. might house America’s chief military strategists, but any tactical mind could appreciate the importance of America’s soccer pentagon to this World Cup campaign.

From The Wall Street Journal ● Jun. 18, 2026

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

Connecting the corners of that pentagon with lines generates a small, upside-down, five-pointed star, which is exactly the same as the original star in its proportions.

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

The Pentagon has said the post by Hegseth "speaks for itself".

From BBC ● Sep. 2, 2026

A parallel panic is also engulfing the Pentagon, where Defense Secretary Pete Hegseth and his loyalists are scrambling to contain a massive internal leak.

From Salon ● Sep. 1, 2026

Reducing munitions production has long been a way for the Pentagon to bank savings when it struggled to pay the bills.

From The Wall Street Journal ● Aug. 30, 2026

There is no standardized US national teaching of 9/11, when 2,977 people died including the passengers and crew of four hijacked planes, victims in New York's Twin Towers, firefighters, and personnel at the Pentagon.

From Barron's ● Aug. 30, 2026

They’d heard of the Pentagon Papers, but hadn’t taken the time to read them.

From "Most Dangerous: Daniel Ellsberg and the Secret History of the Vietnam War" by Steve Sheinkin

It's like jumping into a kaleidoscope, with constantly shifting triangles, pentagons and octagons.

From BBC ● May 25, 2025

This process starts with the assembly of small, triangular parts into hexagons, which subsequently join up with pentagons to form the icosahedral structures of viral capsids.

From Science Daily ● Apr. 4, 2024

If the loop encompasses two adjacent pentagons, then the tile returns to the starting point rotated 120 degrees.

From New York Times ● Jan. 1, 2023

The circles represent End Devices, and the pentagons represent Routers.

From The Verge ● Jul. 29, 2022

For some reason, knowledge of a solid called the dodecahedron having twelve pentagons as sides seemed to them dangerous.

From "Cosmos" by Carl Sagan