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Tetrahedrons and quadrilaterals.
Tetrahedrons are triangular based pyramids that have 4 faces, 6 edges and 4 vertices which were built by the ancient Egyptians.
Tetrahedrons are 4-sided solids. A regular tetrahedron is the equilateral pyramid, having one pyramid as the base and three others the sides.
tetra means four.
Tetrahedrons have many sides.
Two regular tetrahedrons connected face to face make a "regular triangular dipyramid." That is one of the 92 "Johnson solids." Those are the convex polyhedrons whose faces are regular polygons but do not belong to either of the two sets of highly symmetric polyhedrons (the Platonic and the Archimedean) or to the perhaps less interesting two infinite families of prisms and antiprisms. If the two tetrahedrons overlap, both centers at the same place but with the tetrahedrons facing in opposite directions, it makes a "stellated octahedron."
More like two tetrahedrons stuck together.