In the Celtic religion, the modern words Druidry or Druidism denote the practices of the ancient druids, the priestly class in ancient Celtic societies through much of Western Europe north of the Alps and in the British Isles. Druidic practices were part of the culture of all the tribal peoples called Keltoi and Galatai by Greeks and Celtae and Galli by Romans, which evolved into modern English “Celtic” and “Gaulish”. Modern attempts at reconstructing practicing Druidism are called Neo-druidism.
***From what little we know of late druidic practice it appears deeply traditional, and conservative in the sense that the druids were conserving repositories of culture and lore. It is impossible now to judge whether this continuity had deep historical roots and originated in the social transformations of late La Tene time, or whether there had been a discontinuity and a druidic religious innovation. The etymological origins of the word druid are varied and doubtful enough that the word may be pre-Indo-European. The most widespread view is that “druid” derives from the Celtic word for an oak tree (doire in Irish Gaelic), a word whose root also meant “wisdom.”***
***Their influence was as much social as religious. Druids used not only to take the part that modern priests would, but were often the philosophers, scientists, lore-masters, teachers, judges and councillors to the kings. The Druids linked the Celtic peoples with their numerous gods, the lunar calendar and the sacred natural order. With the arrival of Christianity in each area, all these roles were assumed by the bishop and the abbot, who were never the same individual, however, and might find themselves in direct competition.***
Our historical knowledge of the druids is very limited. Druidic lore consisted of a large number of verses learned by heart, and we are told that sometimes twenty years were required to complete the course of study. There may have been a Druidic teaching center on Anglesey (Ynys Mon) centered on magical lakes, but what was taught, whether poetry, astronomy or whether possibly even the Greek language, is conjecture. Of their oral literature of sacred songs, formulas for prayers and incantations, rules of divination and magic, not one verse has survived, even in translation, nor is there even a legend that we can call purely druidic....