What does dihedral mean?
A dihedral is the angle formed where two planes meet, measured along the line at which they intersect. The term is central to several technical fields: geometers use it to describe the angle between the faces of a polyhedron, chemists use it to describe molecular geometry, and aviators use it to describe the upward tilt of an aircraft's wings away from the fuselage. That upward tilt, called positive dihedral, gives an aircraft natural roll stability — if a gust tips one wing, the design tends to bring the plane back to level flight on its own. Derived from Greek roots meaning 'two' and 'seat' or 'base', the word carries a precise, scholarly tone and appears almost exclusively in scientific and engineering contexts. For anyone reading about architecture, crystallography, or aircraft design, 'dihedral' is a small but essential piece of technical vocabulary.
The angle between two intersecting planes, especially as measured in geometry, crystallography, or chemistry.
"The dihedral between the two crystal faces was exactly ninety degrees."
In aeronautics this noun specifically refers to the upward angle of the wings relative to the horizontal.
Relating to, having, or forming a dihedral angle; in aviation, describing wings angled upward from the horizontal.
"The aircraft's dihedral wings made it notably stable in crosswinds."
Commonly used attributively in phrases such as 'dihedral angle' or 'dihedral configuration'.
Used when referring to multiple dihedral angles or multiple instances of wing dihedral across different aircraft or structures.
"The textbook compared the dihedrals of various polyhedra side by side."
The same Greek word for 'seat' that gave us 'cathedral' also names the angle where two planes meet — and it keeps airplanes flying level without the pilot lifting a finger.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dihedral
Dihedral comes from Greek roots: 'di-', meaning 'two', combined with 'hedra', meaning 'seat' or 'base'. The same root 'hedra' produced 'polyhedron' and, through Latin borrowing, 'cathedral' (from 'kathedra', a seat). The word entered English scientific usage in the nineteenth century as mathematicians formalized the study of angles between planes, and it was later adopted by aeronautical engineers to describe wing inclination.
Related word forms
How dihedral is actually used
Primarily technical vocabulary used in mathematics, crystallography, chemistry, and aviation. In everyday speech it is rare outside these fields. When used attributively ('dihedral angle', 'dihedral wing'), it functions as an adjective.
Easily confused with dihedral
Anhedral is the opposite configuration, where the wings angle downward rather than upward from the fuselage.