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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Congress must approve the long-term deals and funding before the Pentagon can lock in contracts.
From Barron's • Jun. 17, 2026
Rush allegedly conducted a fake briefing with two co-workers on the supposed program, which he claimed was run jointly with the Pentagon.
From The Wall Street Journal • Jun. 16, 2026
The Pentagon has asked Congress for $500 million next year to improve prepositioning of equipment and fuel across the Asia-Pacific to deter China.
From Barron's • Jun. 16, 2026
The Pentagon has also rejected any role in the sinking of a third Ecuadorean fishing vessel — the Fiorella, which disappeared on the afternoon of Jan. 20 with eight crew members on board.
From Los Angeles Times • Jun. 15, 2026
They’d read it right away, the senator said, and set up a public hearing of the Senate Foreign Relations Committee—a dramatic setting in which to unveil the Pentagon Papers to the American people.
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.
