-gon

-gon

(word root) angle
Examples of words with the root -gon: pentagon
Abused, Confused, & Misused Words by Mary Embree Copyright © 2007, 2013 by Mary Embree

-gon

suff.
A figure having a specified kind or number of angles: isogon.

[Latin -gōnum, from Greek -gōnon, from neuter of -gōnos, angled, from gōniā, angle; see genu- in Indo-European roots.]
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.

-gon

n combining form
indicating a figure having a specified number of angles: pentagon.
[from Greek -gōnon, from gōnia angle]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

-gon

a combining form used in the names of geometrical figures having the number or sort of angles specified by the initial element: isogon; polygon.
[< Greek -gōnon, n. use of neuter of -gōnos, akin to gōnía angle, góny knee]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.