Dihedral

a.	1.	Having two plane faces; as, the dihedral summit of a crystal.
	2.	Of a kite or an aëroplane, having wings that make with one another a dihedral angle, esp. when the angle between the upper sides is less than 180°.
	3.	(Aëronautics) Of wing pairs, inclined at an upward angle to each other. Dihedral angle the angular space contained between planes which intersect. It is measured by the angle made by any two lines at right angles to the two planes.