polygonregular (left) and irregular (right) polygonspol·y·gon (p?l??-g?n?)n. A closed plane figure bounded by three or more line segments.[Late Latin polyg?num, from Greek polug?non, from neuter of Greek polug?nos, polygonal : polu-, poly- + -g?nos, angled; see -gon.]po·lyg?o·nal (p?-l?g??-n?l) adj.po·lyg?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.polygon (?p?l????n) n (Mathematics) a closed plane figure bounded by three or more straight sides that meet in pairs in the same number of vertices, and do not intersect other than at these vertices. The sum of the interior angles is (n?2) × 180° for n sides; the sum of the exterior angles is 360°. A regular polygon has all its sides and angles equal. Specific polygons are named according to the number of sides, such as triangle, pentagon, etc[C16: via Latin from Greek polug?non figure with many angles] polygonal adj po?lygonally advCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014pol?y?gon (?p?l i?g?n) n. a figure, esp. a closed plane figure, having three or more, usu. straight, sides. [1560?70;