[1] : The Collaborative International Dictionary of English v.0.48

diametric \diam"etric\, diametrical \diam"etrical\, a.
   1. of or pertaining to a diameter.
      1913 webster

   2. as remote as possible, as if at the opposite end of a
      diameter; directly adverse.
      1913 webster

[2] : WordNet (r) 2.0

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
see also:
diametral diametric opposite polar 

Diametrical >> D Words
Diametrical, definition of term: Diametrical
diametrical_pag1.html