diametral surface

from The Collaborative International Dictionary of English v.0.48

Diametral \Di*am"e*tral\, a. [Gr. F. diam['e]tral.]
   Pertaining to a diameter; diametrical.
   [1913 Webster]

   {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.
      [1913 Webster]