Source : Webster's Revised Unabridged Dictionary (1913)

Diametrically \Di*am"e*tric*al*ly\, adv.
   In a diametrical manner; directly; as, diametrically
   opposite.

         Whose principles were diametrically opposed to his.
                                                  --Macaulay.

Source : WordNet®

diametrically
     adv : as from opposite ends of a diameter; "when two honest
           witnesses give accounts of the same event that differ
           diametrically, how can anyone prove that the evidence
           you gave was deliberately false?"; "three of these
           brushes were approximately 120 feet apart and the
           fourth diametrically opposite to one of the three"