Dictionary:

diametrical

  (dī'ə-mĕt'rĭ-kəl) also diametric (-rĭk)

1. Of, relating to, or along a diameter.
2. Exactly opposite; contrary.

adjective

Diametrically opposed: antipodal, antipodean, antithetical, antonymic, antonymous, contradictory, contrary, converse², counter, diametric, opposing, opposite, polar, reverse. See support/oppose.

The adjective has 2 meanings:

Meaning #1: related to or along a diameter
  Synonyms: diametral, diametric
  Pertains to noun: diameter (meaning #2)

Meaning #2: characterized by opposite extremes; completely opposed
  Synonyms: diametric, opposite, polar