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[pen-tuh-gon, -guh n] /ˈpɛn təˌgɒn, -gən/
a polygon having five angles and five sides.
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.
Origin of pentagon
1560-70; < Late Latin pentagōnum < Greek pentágōnon, noun use of neuter of pentágōnos five-angled. See penta-, -gon
Related forms
[pen-tag-uh-nl] /pɛnˈtæg ə nl/ (Show IPA),
pentagonally, adverb
subpentagonal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for pentagon


a polygon having five sides
Derived Forms
pentagonal (pɛnˈtæɡənəl) adjective


the five-sided building in Arlington, Virginia, that houses the headquarters of the US Department of Defense
the military leadership of the US
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for pentagon

plane figure with five angles and five sides, 1560s, from Middle French pentagone or directly from Late Latin pentagonum "pentagon," from Greek pentagonon, noun use of neuter of adjective pentagonos "five-angled," from pente "five" (see five) + gonia "angle" (see knee (n.)). The U.S. military headquarters Pentagon was completed 1942, so called for its shape; used allusively for "U.S. military leadership" from 1945. Related: Pentagonal.

In nature, pentagonal symmetry is rare in inanimate forms. Packed soap bubbles seem to strive for it but never quite succeed, and there are no mineral crystals with true pentagonal structures. But pentagonal geometry is basic to many living things, from roses and forget-me-nots to sea urchins and starfish. [Robert Bringhurst, "The Elements of Typographic Style," 1992]

Online Etymology Dictionary, © 2010 Douglas Harper
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pentagon in Science
A polygon having five sides.

pentagonal adjective (pěn-tāg'ə-nəl)
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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pentagon in Culture

Pentagon definition

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

Note: 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.”
Note: The Pentagon was severely damaged by the September 11 attacks.

pentagon definition

A polygon having five sides.

Note: The Pentagon is a huge five-sided building near Washington, D.C., that contains offices of the Department of Defense.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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