dihedral

n. angle between an aircraft wing and the horizontal; angle that is formed by two planes (Mathematics)

adj. having two plane faces (Mathematics)

Dihedral is the upward angle from horizontal in a fixed-wing aircraft or bird wing from root to tip, as viewed from directly in front or behind the aircraft. The aeorodynamic stabilising qualities of the dihedral were first described by Sir George Cayley in 1808/09. Downward angled wings have negative dihedral, or anhedral. Wings with local dihedral angles that change along the span are polyhedral.
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adj. dihedral

(a.)
Having two plane faces; as, the dihedral summit of a crystal.
  

dihedral
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