[voc.a.tive] adj [ME vocatif, fr. MF, fr. L vocativus, fr. vocatus, pp. of vocare] (15c) 1: of, relating to, or being a grammatical case marking the one addressed (as Latin Domine in miserere, Domine "have mercy, O Lord")
2. of a word or word group: marking the one addressed (as mother in "mother, come here") -- voc.a.tive.ly adv
[2]vocative n (ca. 1522) 1: the vocative case of a language
2: a form in the vocative case