The Palantir of Westernesse was a quest artifact from versions of NetHack prior to 3.3.0. This was the version which introduced a choice of starting races, so the old Elf class was removed, along with its quest and quest artifact.
The Palantir of Westernesse was a crystal ball. When carried, it granted regeneration, ESP, and half magic-damage. When invoked, it tamed nearby creatures.
It does reappear in Slash'EM Extended though, which has an Elph role that is basically a remake of the old Elf role. In that variant, the Palantir of Westernesse is the Elph quest artifact.