Name this figure!

Factual Questions
1

What is the name for a regular polyhedron with twenty triangular faces?

2

dodecahedron

3

Are you sure it’s not an icosahedron? Isn’t a dodecahedron 12-sided?

4

dammit!

5

dodecahedron. A polyhedron with 12 faces.

icosahedron. A polyhedron having 20 faces.

– Reference: dictionary.com

6

Yeah, yeah I screwed up. However, technically the OP is looking for a regular icosahedron, unless there is another word that means specifically that.

7

As a roleplayer, this is right up my street.

I use the following:

4-sided pyramid
6-sided cube
8-sided octogon
12-sided dodecahedron
20-sided icosohedron

(I may have muddled the names in naming solid versions, but I’m certain my prefixes are correct. :confused: )

8

Try octohedron and tetrahedron for the 4- and 8-sided dice, respectively.

9

Other way around, ultrafilter.

10

Although a tetrahedron is a type of pyramid, specifically an equilateral triangular-based pyramid. Also note that the terms “tetrahedron”, “icosohedron”, etc. don’t necessarily imply any degree of regularity, just a number of faces. If, for instance, you take a cube and lop off two of the corners, the resulting figure will be an octahedron, just a very irregular one. Similarly, a ten-sided die could properly be called a decahedron (note no do- at the beginning).

11

Here are some pretty pictures and interactive models of all five Platonic solids, including the regular icosahedron.

If you don’t care about the triangular faces being identical (the OP doesn’t specify), then there’s also Jessen’s orthogonal icosahedron, which still counts as a regular polyhedron. They make lousy dice however.

12

Bytegeist
I don’t believe Jessen’s orthogonal icosahedron is a regular polyhedron.
I also believe that there are only 5 regular polyhedra. (The ones listed by glee and then corrected by Chronos).

13

Ah, you’re right — in the first part certainly. Although, according to here, the term “regular polyhedron” can sometimes include these four concave polyhedra. None of them has 20 sides though.

In any case, the Jessen’s orthogonal icosahedron doesn’t fit either sense of the term, so I stand corrected.