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.

1560–70; < Late Latin pentagōnum < Greek pentágōnon, noun use of neuter of pentágōnos five-angled. See penta-, -gon

pentagonal [pen-tag-uh-nl] , adjective
pentagonally, adverb
subpentagonal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
pentagon (ˈpɛntəˌɡɒn)
a polygon having five sides

Pentagon (ˈpɛntəˌɡɒn)
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 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

plane figure with five angles and five sides, 1570, from M.Fr. pentagone, from L.L. pentagonum "pentagon," from Gk. pentagonon, properly neut. of adj. pentagonos "five-angled," from pente "five" + gonia "angle" (see knee). The U.S. military headquarters Pentagon was completed
1942, so called for its shape; used allusively for "U.S. military leadership" from 1945.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
pentagon   (pěn'tə-gŏn')  Pronunciation Key 
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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American Heritage
Cultural Dictionary

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 American Heritage® 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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