undecagon
/ʌnˈdɛkəɡ(ə)n
/noun
Another term for hendecagon.These various polygon shapes consist of, but are not limited to, triangles, squares, pentagons, hexagons, heptagons, octagons, nonagons, decagons, undecagons, and dodecagons....
- How many diagonals are needed to divide a heptagon, a nonagon, and an undecagon into triangles?
Origin
Early 18th century: formed irregularly from Latin undecim 'eleven', on the pattern of decagon.