I am a grade 8 teacher and have come across the term "Triakis" used with Tetrahedron, octahedron, and hexahedron. What does this term refer to, and what's the difference between a triakis polyhedron and one that is not?

I'd also like to know what is meant by the term antiprism, as opposed to prism.

Hi Anne,

The online version of the Oxford English Dictionary, under triakis, has

names of solids derived respectively from the icosahedron, octahedron, and tetrahedron by erecting a triangular pyramid on each face, thus multiplying the original number of faces by three. (In Geom. specially applied to those forms in which the pyramids are of such altitude as to make all the solid angles regular.) Hence in derived adjs., as triakisoctahedrid. There is a java applet of a triakistetrahedron at http://polytopes.wolfram.com/archimedean/duals/A13Dual.html This page also has a template that you can print, cut out and fold into a triakistetrahedron

Something interesting that I found when seraching for the word triakis is that the Leopard Shark is Triakis semifasciata The name makes me wonder if its teeth are in the shape of triangular pyramids.

You can find a definition of an antiprism at http://euch3i.chem.emory.edu/proposal/www.li.net/~george/virtual-polyhedra/prisms-info.html

Note:I asked a colleague, Alec Couros, if he knew the meaning of the word triakis and he sent me the following note.

actually ... here is some new insight:
http://www.dohenystatebeach.org/nn-ramblings%20from%20the%20ranger.htm
Scroll down to 'leapord shark" - 2nd last paragraph. I think this answers the question. The pertinent piece of that paragraph is: Triakis is Greek for three pointed, referring to this shark's three pointed teeth,

Cheers,
Penny
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