An Etymological Dictionary of Astronomy and Astrophysics

1. Geometry: A three-dimensional figure formed by several → polygons.
   

2. A set P ⊆ ℜⁿ is a polyhedron if there is a system of finitely many unequalities Ax ≤ b such that P = {x ∈ ℜⁿ | Ax ≤ b}.

See also: → poly-; → hedron.