Dis forDiamond
A diamond, or rhombus is a four-sided shape, like a square turned on its side. All four sides of a rhombus are the same length but the angles on the corners do not have to be 90 degrees like in a square, the rhombus can be taller than it is wide or wider than it is tall.
The window in the picture is diamond-shaped.
A diamond is also a kind of precious stone.