noun
trigonal pyramid
Technical term in geometry and crystallography for a pyramid with a triangular base.
三方錐は、底面が三角形のピラミッド形である。
A trigonal pyramid is a pyramid shape with a triangular base.
Compound of 三 (three), 方 (direction), and 錐 (pyramid/cone). The exact historical derivation is uncertain; the term is used in technical fields.