Definition of dual:
		
		
		(adj) :
		
		characterized by having two (usually equivalent) components; double
		
								
			
	
		
		
		(n) :
		
		of an item that is one of a pair, the other item in the pair; of a 
regular polyhedron with V vertices and F faces, the regular polyhedron having F vertices and V faces
		
 
								
				"the tetrahedron is the dual of the cube."