Entry 1 sense Webster, 1913 Diametrically · Di·am·e·tric·al·ly · IPA /ˌdaɪ.əˈmɛt.ɹɪk.li/ 01 adv. In a diametrical manner; directly; as, diametrically opposite. 1. In a diametrical manner; directly; as, diametrically opposite. “Whose principles were diametrically opposed to his.” — Macaulay.