noun
polyhedron
Technical term in geometry for a solid bounded by flat polygonal faces.
立方体は六つの正方形の面を持つ多面体です。
A cube is a polyhedron with six square faces.
多角形 is a polygon (2D), while 多面体 is a polyhedron (3D).
Compound of 多 (many) + 面 (face) + 体 (body), a straightforward kanji-based term for a solid with many faces.