1) Dihedral angle 
Usually a regular dihedron is implied (two regular polygons) and this gives it a Schläfli symbol as {n,2}. The dual of a n-gonal dihedron is the n-gonal hosohedron, where n digon faces share two vertices. ==As a polyhedron== A dihedron can be considered a degenerate prism consisting of two (planar) n-sided polygons connected `back-to-back`, so .....
• (n.) A figure with two sides or surfaces.
Di·he'dron noun [ See Dihedral .] A figure with two sides or surfaces. Buchanan. 
a figure formed by two intersecting planes. Also called