Dihedral \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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Dihedral \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.

Source: Webster's Revised Unabridged Dictionary (1913)