early 15c., "showing the person or thing spoken to," from Middle French vocatif, from Latin vocativus (casus) "(case of) calling," from vocatus, past participle of vocare "to call," which is related to vox (genitive vocis) "voice" (from PIE root *wekw- "to speak"). The Latin is a translation of Greek kletike ptosis, from kletikos "related to calling," from kletos "called." As a noun from 1520s.
