Druids, a sacred order of learned men under a chief called the Archdruid, among the ancient Celtic nations, particularly of Gaul and Britain, who, from their knowledge of the arts and sciences of the day, were the ministers of religion and justice, as well as the teachers of youth to the whole community, and exercised an absolute control over the unlearned people whom they governed; they worshipped in oak groves, and the oak tree and the mistletoe were sacred to them; the heavenly bodies appear to have been also objects of their worship, and they appear to have believed in the immortality and transmigration of the soul; but they committed nothing to writing, and for our knowledge of them we have to depend on the reports of outsiders.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Droz, Gustav * Drumclog Moss