Polygons: How Many Sides?
Updated February 21, 2017 | Factmonster Staff 
A geometrical figure with three or more sides is called a polygon or a polyhedron. Here are the names for some polygons.
| 3 | triangle, trigon |
| 4 | quadrilateral, tetragon |
| 5 | pentagon |
| 6 | hexagon |
| 7 | heptagon |
| 8 | octagon |
| 9 | nonagon, enneagon |
| 10 | decagon |
| 11 | hendecagon |
| 12 | dodecagon, duodecagon |
| 13 | triskaidecagon, tridecagon |
| 14 | tetrakaidecagon, tetradecagon |
| 15 | pentadecagon |
| 16 | hexadecagon |
| 17 | heptadecagon |
| 18 | octadecagon |
| 19 | enneadecagon |
| 20 | icosagon |
How Many Angles?
A polygon has as many angles as it has sides. For example, a triangle has 3 sides and 3 angles. A pentagon has 5 sides and 5 angles. An octadecagon has 18 sides and 18 angles!
