noun
pentagonal pyramid
A pyramid with a pentagonal base. Used in geometry and mathematics.
五角錐の体積を計算する公式を覚えていますか。
Do you remember the formula for calculating the volume of a pentagonal pyramid?
三角錐 is a triangular pyramid (tetrahedron), while 五角錐 has a pentagonal base.
Compound of 五角 (pentagon) + 錐 (pyramid, cone). The reading is on'yomi.