Source : Webster's Revised Unabridged Dictionary (1913)

Pentahedron \Pen`ta*he"dron\, n. [Penta- + Gr. "e`dra seat,
   base.]
   A solid figure having five sides.

Source : WordNet®

pentahedron
     n : any polyhedron having five plane faces
     [also: {pentahedra} (pl)]