The Collaborative International Dictionary of English v.0.48:

Polyhedron \Pol`y*he"dron\, n.; pl. E. Polyhedrons., L.
   Polyhedra. [NL., fr. Gr. ? with many seats or sides; poly`s
   many + ? a seat or side: cf. F. poly[`e]dre.]
   1. (Geom.) A body or solid contained by many sides or planes.
      [1913 Webster]

   2. (Opt.) A polyscope, or multiplying glass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

polyhedron
    n 1: a solid figure bounded by plane polygons or faces