rhombohedron

from WordNet (r) 3.0 (2006)

rhombohedron
    n 1: a parallelepiped bounded by six similar faces (either
         rhombuses or parallelograms)

from The Collaborative International Dictionary of English v.0.48

Rhombohedron \Rhom`bo*he"dron\, n. [NL., fr. Gr. ??? rhomb + ???
   seat, base.] (Geom. & Crystallog.)
   A solid contained by six rhomboids; a parallelopiped.
   [1913 Webster]