\Di*he"dral\, a. [Gr. di- = di`s- twice + ? a seat,
bottom, base, fr. ? to sit. Cf. {Diedral}.]
Having two plane faces; as, the dihedral summit of a crystal.
{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.

\Di*he"dral\, a.
1. Of a kite or an a["e]roplane, having wings that make with
   one another a dihedral angle, esp. when the angle between
   the upper sides is less than 180[deg].
2. (A["e]ronautics) Of wing pairs, inclined at an upward
   angle to each other.