A pyramid, with a triangular base.
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It could be a cone
A truncated tetrahedron.
I cannot think of any 2-d shape. The 3-d shape with four faces is a tetrahedron.
Tetra = four. It is a 3-d shape with 4 faces.
An octahedron is a closed 3-d shape with 8 polygonal faces. There are 257 topologically different convex octahedra. They can have faces which are triangles, quadrilaterals, pentagons, hexagons or heptagons,