The Eilt Druin is a Druid talisman. It is a medallion cast with the insignia of the Druids, that of a fist holding forth a burning torch. "Eilt Druin" is an Elven phrase that translates to "Through knowledge, power" or "Through truth, power." It is the Druid credo.
The Eilt Druin is the symbol of office for the Ard Rhys and was given to Galaphile, founder of the Druid Order, according to The World of Shannara. It was forged from gold strengthened with a small amount of alloys, using knowledge from the Old World, and laced with silver trappings.
The medallion was last worn by Athabasca, who was Ard Rhys before the start of the Second War of the Races. After Athabasca was killed by Brona, the Eilt Druin was left unclaimed at Paranor. Bremen, acting on a vision sent to him by Galaphile's shade, returned to Paranor and recovered the Eilt Druin. He had it set into the hilt of the Sword of Shannara at the time of the Sword's forging.
Bremen then took the Sword to the Hadeshorn, where the shades of Druids past gathered to transfer the truth they had found in life to the Sword through the Eilt Druin, imbuing the Sword with the magical properties that allowed it to become anathema to the Warlock Lord. The Sword was first used by the Elven King Jerle Shannara, from whom it received its name.
Centuries later, Grianne Ohmsford, founder and Ard Rhys of the Third Druid Order, had a new medallion created as a sign of her high office. She wore it into her final battle against the mutinous Druid faction led by Shadea a'Ru. However, there is no indication that Grianne's Eilt Druin possessed magical properties, and it is unclear what became of her medallion after Grianne dispersed the Druid Council and gave herself over to the Tanequil.