vocative
Concise Oxford English Dictionary © 2008 Oxford University Press:
vocative /ˈvɒkətɪv/ Grammar
▶adjective relating to or denoting a case of nouns, pronouns, and adjectives used in addressing or invoking a person or thing. ▶noun a word in the vocative case.
– origin ME: from OFr. vocatif, -ive or L. vocativus, from vocare ‘to call’.
'vocative' also found in these Oxford entries:

