Master-stone

The chief of all the palantíri, both in Aman and Middle-earth, which was held in the Tower of Avallónë on the Lonely Isle of Tol Eressëa. It was said that the Seeing-stone in Elostirion in the Tower Hills could be used to look back along the Straight Road and glimpse the Masterstone's Tower.

The Stone of Avallónë is variously named the 'Masterstone' or Master-stone. Confusingly, there was also a 'Master Stone', the palantír of Osgiliath, but this was a lesser Stone than the Masterstone in Avallónë, having power only over other palantíri in Middle-earth.