noun
monogon; henagon
A one-sided polygon in geometry; a theoretical shape with one vertex and one edge. Rarely encountered outside mathematical contexts.
一角形は、ユークリッド幾何学では通常考えられない図形だ。
A monogon is a shape not normally considered in Euclidean geometry.
球面上では、一角形を定義できる場合がある。
On a sphere, a monogon can sometimes be defined.
Compound of 一 (one) + 角 (angle) + 形 (shape). The reading いちかくけい is regular; いっかっけい is a less common euphonic variant.