Source : Webster's Revised Unabridged Dictionary (1913)

Diametric \Di*am"e*tric\, Diametrical \Di*am"e*tric*al\, a.
   1. Of or pertaining to a diameter.

   2. As remote as possible, as if at the opposite end of a
      diameter; directly adverse.

Source : WordNet®

diametrical
     adj 1: related to or along a diameter; "the diametral plane" [syn:
            {diametral}, {diametric}]
     2: characterized by opposite extremes; completely opposed; "in
        diametric contradiction to his claims"; "diametrical (or
        opposite) points of view"; "opposite meanings"; "extreme
        and indefensible polar positions" [syn: {diametric}, {opposite},
         {polar}]