vocative
 oxford
 views  updated Jun 08 2018voc·a·tive  / ˈväkətiv/  Gram. • adj. relating to or denoting a case of nouns, pronouns, and adjectives in Latin and other languages, used in addressing or invoking a person or thing.• n. a word in the vocative case. ∎  (the vocative) the vocative case.
 The Oxford Pocket Dictionary of Current English