noun
nonagon; enneagon
Geometric term for a nine-sided polygon. 九角形 is the standard Japanese term; ノナゴン (nonagon) is also used in some contexts.
九角形の内角の和は1260度です。
The sum of the interior angles of a nonagon is 1260 degrees.
この図形は九角形
This shape is a nonagon.
Octagon (eight-sided polygon); 九角形 has one more side.
Decagon (ten-sided polygon); 九角形 has one fewer side.
Compound of 九 (kyū, 'nine') + 角形 (kakukei, 'polygon'), literally 'nine-angled shape'.