- Druid 1560s, from Fr. druide, from L. druidae (pl.), from Gaulish Druides, from O.Celt. *derwijes, probably representing O.Celt. derwos "true" and *dru- "tree" (especially oak) + *wid- "to know" (Cf. vision). Hence, lit., perhaps, "they who know the oak" (perhaps in allusion to divination from mistletoe). Anglo-Saxon, too, used identical words to mean "tree" and "truth" (treow).The English form comes via Latin, not immediately from Celtic. The Old Irish form was drui (dat. and acc. druid; pl. druad); Mod.Ir. and Gael. draoi, gen. druadh "magician, sorcerer." Not to be confused with United Ancient Order of Druids, secret benefit society founded in London 1781.
Etymology dictionary. 2014.