The Etymology of Druid
Druid entered English in 1563 from Latin druidae, the term Caesar and Pliny used for the priestly caste of Gaulish and British Celts. Caesar describes them in De Bello Gallico as judges, teachers, sacrificers, and memorisers of immense oral lore, forbidden to commit their knowledge to writing. The Latin form descends from a Proto-Celtic *druwid-, which is traditionally analysed as oak-knower, combining the PIE roots *dóru- (oak, tree, also giving English tree and Greek drys) and *weid- (to see, know, also giving English wit and Latin videre). Pliny supports the oak reading by reporting that druids revered oak groves and harvested mistletoe from them. The reconstruction is widely cited but disputed: some Celticists argue the first element is an intensifying prefix (very-knower, true-knower) rather than a literal oak. Modern Irish draoi and Welsh derwydd preserve the same Celtic stem.