The Collaborative International Dictionary
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.
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].
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(A["e]ronautics) 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.
Wiktionary
n. (context geometry English) The angle between two planes.
Wikipedia
A dihedral angle is the angle between two intersecting planes. In chemistry it is the angle between planes through two sets of three atoms, having two atoms in common. In solid geometry it is defined as the union of a line and two half-planes that have this line as a common edge. In higher dimension, a dihedral angle represents the angle between two hyperplanes.
Usage examples of "dihedral angle".
The old hands all believed that by screwing up the rigging wires and increasing the dihedral angle of the wings, they could put a few knots on their speed.