decahedron
A polyhedron with ten faces. Used in geometry.
It is known that a regular decahedron does not exist.
This crystal has the shape of a decahedron.
正多面体 means regular polyhedron; a regular decahedron (正十面体) does not exist, so 十面体 usually refers to an irregular decahedron.
icosahedron
Compound of 十 (ten), 面 (face), and 体 (body). A straightforward kanji-based term for a ten-faced solid.