a polygon having five angles and five sides.
the Pentagon,
a building in Arlington, Virginia, having a plan in the form of a regular pentagon, containing most U.S. Defense Department offices.
the U.S. Department of Defense; the U.S. military establishment.
the five-sided building in Arlington, Virginia, that houses the headquarters of the US Department of Defense
the military leadership of the US
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.
1560–70; < Late Latin pentagōnum < Greek pentágōnon, noun use of neuter of pentágōnos five-angled. See penta-, -gon
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.
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Many of the bills were spurred by AI developer Anthropic’s recent spat with the Pentagon, which raised questions about the Defense Department’s guardrails for keeping a human involved when AI is used.
From The Wall Street Journal • Jun. 8, 2026
This year’s list also removes about 10 businesses that were on prior lists that the Pentagon said no longer qualified as Chinese military entities.
From The Wall Street Journal • Jun. 8, 2026
A Defense Department spokesperson said the Pentagon took the list down to review it for updates, and published a new list after making changes.
From The Wall Street Journal • Jun. 8, 2026
I can think of one case where a senior civilian in the Pentagon manipulated the promotion process to make sure that certain colonels were lifted to the rank of general.
From Slate • Jun. 5, 2026
Years later, after the Nixon presidency had come crashing down, Kissinger would claim he had never had strong feelings one way or the other about the Pentagon Papers.
From "Most Dangerous: Daniel Ellsberg and the Secret History of the Vietnam War" by Steve Sheinkin
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
