1. A polyhedron formed by joining two pyramids base-to-base, having two apex vertices and a shared polygonal base.
Usage: geometry; also called dipyramid
2. A crystal form consisting of two pyramids joined at their bases, common in mineral crystallography.
Usage: crystallography; mineralogy

Examples

• A triangular bipyramid has six triangular faces and five vertices.
• The hexagonal bipyramid is a common crystal form in nature.
• In geometry class, students learned to construct a bipyramid by stacking two square pyramids.
• Quartz crystals often display a bipyramid shape with pointed ends.
• The octahedron is a special case of a square bipyramid.
• A pentagonal bipyramid has ten triangular faces.