Source : Webster's Revised Unabridged Dictionary (1913)

Diametral \Di*am"e*tral\, a. [Gr. F. diam['e]tral.]
   Pertaining to a diameter; diametrical.

   {Diametral curve}, {Diametral surface} (Geom.), any line or
      surface which bisects a system of parallel chords drawn in
      a curve or surface.

   {Diametral planes} (Crystal.), planes in which two of the
      axes lie.

Diametral \Di*am"e*tral\, n.
   A diameter. [Obs.] --Sir T. Browne.

Source : WordNet®

diametral
     adj : related to or along a diameter; "the diametral plane" [syn:
           {diametric}, {diametrical}]