Answer: dihedral

AnswerCrossword Clue
dihedralhaving or formed by two planes
dihedralthe angle at which the right and left wings or the halves of any other horizontal surface of an airplane or the like are inclined upward or downward
dihedralthe angle between two planes, also DIEDRAL
dihedralfigure formed by two intersecting planes
dihedralof or pertaining to a dihedron