The earliest Latin writers used vates to denote "prophets" and soothsayers in general; the word fell into disuse in Latin until it was revived by Virgil *. Then Ovid could describe himself as the vates of Eros (Amores 3.9).
According to Strabo Diodorus Siculus Poseidonius, the vates (ουατεις) were one of three classes of Celtic priesthood, the other two being the druids and the bards. The Vates had the role of seers and performed the sacrifice, under the presidence of a druid. Their role was therefore corresponding to that of an Adhvaryu in Vedic religion. Celtic Vates is continued by Irish fáith "prophet, seer"[http://www.kernunnos.com/culture/druids/vates.html" target="_blank" >*.
It is unknown whether the Latin and Gaulish usages are cognates, or if the former should be considered a Celtic loanword. The word may be derived from a PIE root *wāt "to inspire, spiritually arouse", however that root may not be as old as Proto-Indo-European, since it is only certainly attested for Celtic and Germanic (but it may be present natively in Italic, and possibly also in Greek and Indo-Iranian). Virgil uses the Latin vannus "winnowing fan" (from *wat-nos, compare Old High German wadal, modern German Wedel, with the same meaning, from *wat-lo) for something borne about in the Bacchic festival, suggesting that the root may have had an ecstatic sense in Italic also.
Rübekeil (2003) suggested that the name of the Germanic god *Wōđinaz may in fact be an early loanword, an adjective *vatinos based on Celtic vates.
Vates, or Ovates, make up one of the three grades of the Order of Bards, Ovates and Druids, a Neo-druidry order based in England.