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1. A polygon with five sides and five angles.
2. Pentagon A five-sided building near Washington DC, containing the US Department of Defense and the offices of the US Armed Forces. Used with the.

[Late Latin pentagōnium, from Greek pentagōnon, from neuter of pentagōnos, pentagonal : penta-, penta- + -gōnos, angled; see -gon.]

pen·tag′o·nal (pĕn-tăg′ə-nəl) adj.
pen·tag′o·nal·ly adv.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Mathematics) geometry in a pentagonal manner; in the fashion of a pentagon
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
Kitaev, "Role of poly(vinylpyrrolidone) (PVP) and other sterically protecting polymers in selective stabilization of {111} and {100} facets in pentagonally twinned silver nanoparticles," Chemical Communications, vol.
Chorion was hexagonally and pentagonally reticulated (Figure 2(b)) except for the micropilar area, which was rosette-like, composed by five petaloid cells (Figure 2(c)).
The same reasoning ensures that Timaeus' pentagonally defined cosmos will not be dissolved into its triangularly defined components (thus overcoming geometrically the cyclical cosmology of Empedocles), and in this way his universe is everlastingly secure.