The Collaborative International Dictionary of English v.0.48:

Hexahedron \Hex`a*he"dron\, n.; pl. E. Hexahedrons, L.
   Hexahedra. [Hexa- + Gr. ? seat, base, fr. ? to sit: cf. F.
   hexa[`e]dre.] (Geom.)
   A solid body of six sides or faces.
   [1913 Webster]

   Regular hexahedron, a hexagon having six equal squares for
      its sides; a cube.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hexahedron
    n 1: any polyhedron having six plane faces