Diagonal

In geometry, a diagonal is a line segment joining two vertices of a polygon or polyhedron, when those vertices are not on the same edge. Informally, any sloping line is called diagonal. The word diagonal derives from the ancient Greek διαγώνιος diagonios, "from corner to corner" ; it was used by both Strabo and Euclid to refer to a line connecting two vertices of a rhombus or cuboid, and later ado... (Wikipedia)