1723, from assumed Latin plural Ovatēs, from Greek Ouateis "soothsayers, prophets," mentioned by Strabo as a third order in the Gaulish hierarchy, from Proto-Celtic *vateis, plural of *vatis, cognate with Latin vatis, Old Irish faith, Welsh ofydd. The modern word, and the artificial senses attached to it, are from the 18c. Celtic revival and appear first in Henry Rowlands.
Now an ofydd, or, as the word is sometimes rendered into English, ovate, is commonly understood to mean an Eisteddfodic graduate who is neither a bard nor a druid; but formerly it appears to have meant a man of science and letters, or perhaps more accurately a teacher of the same. [John Rhys, "Lectures on Welsh Philology," 1877]