Druids
2 of the 7 encyclopedias on this shelf carry an entry for Druids. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
an order of priests among the ancient Britons and Gauls. Little is known of them. The best account is found in the sixth book of Caesar's Gallic War. Like the Hebrew tribe of Levi, they were exempt from taxes and military service. They practiced their rites in the recesses of oak groves and held the mistletoe in reverence. Some have tried to picture the Druids as corresponding to the Magi or wise men of the Persians, conjecturing that the rites of the Magi and of the Druids originated in a common source. The dolmens and circles of stones, such as are found at Stonehenge, were formerly considered druidical remains; but they are now thought to be the work of a stone age preceding the Celts. Among much that is misty we are certain of a few facts. The druidic priesthood withstood the Romans with fanatic zeal, reminding the reader of Tecumseh's brother, the prophet who brought on the battle of Tippecanoe. At all events, the Romans found it necessary to hunt out the Druids, cut down their sacred groves, and exterminate them before they could reduce Gaul and Britain to anything like quiet. The Isle of Mona, now Anglesea, was the headquarters-the sacred seat of druidism-in the British Isles. See Boadicea ; Celts
Collier's New Encyclopedia (1921)
the priests of the Celts of Gaul and Britain. According to Julius Cæsar, they possessed the greatest authority among the Celtic nations. They had some knowledge of geometry, natural philosophy, etc., superintended the affairs of religion and morality, and performed the office of judges. They venerated the mistletoe when growing on the oak, a tree which they likewise esteemed sacred. They had a common superior, who was elected by a majority of votes from their own number, and who enjoyed his dignity for life. Of their religious doctrines little is known. Human sacrifice was one of their characteristic rites, the victims being usually prisoners of war.