heptagon

The students learned that a heptagon has seven equal sides.

用法提示：名词作宾语从句主语，表示七边形这一几何图形。

He drew a regular heptagon on the blackboard.

用法提示：名词作宾语，描绘具体图形。

The building's base is designed as a heptagon.

用法提示：名词作介词宾语，指建筑形状。