deltahedron

From delta (Greek letter) +‎ -hedron referring to the triangular shape of the letter.

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deltahedron (plural deltahedrons or deltahedra)

1. (geometry) A polyhedron whose faces are all equilateral triangles.

   There are infinitely many deltahedra, but only eight that are convex.

• Not to be confused with the deltohedron, whose faces are kites.

• deltahedral

• on the ladder