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[pen-tuh-gon, -guh n]
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  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.

Origin of pentagon

1560–70; < Late Latin pentagōnum < Greek pentágōnon, noun use of neuter of pentágōnos five-angled. See penta-, -gon
Related formspen·tag·o·nal [pen-tag-uh-nl] /pɛnˈtæg ə nl/, adjectivepen·tag·o·nal·ly, adverbsub·pen·tag·o·nal, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for pentagon

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British Dictionary definitions for pentagon


  1. a polygon having five sides
Derived Formspentagonal (pɛnˈtæɡənəl), adjective


  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
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

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

pentagon in Science


  1. A polygon having five sides.
Related formspentagonal adjective (pĕn-tăgə-nəl)
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

pentagon in Culture


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


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.


A polygon having five sides.


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 Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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