Source : Webster's Revised Unabridged Dictionary (1913)

Icositetrahedron \I`co*si*tet`ra*he"dron\, n. [Gr. ? twenty + ?,
   combining form of ? four + ? seat, base.] (Crystallog.)
   A twenty-four-sided solid; a tetragonal trisoctahedron or
   trapezohedron.