One of the beacon hills of Gondor, a name “of forgotten origin” and therefore probably pre-Númenórean (LotR/1129). This name may share its initial element with Eilenaer and its final element with Arnach. When the name first appeared in Lord of the Rings drafts, it was written Elenach (WR/232).
Sindarin
Eilenach
Eilenach
On the origin of the name, Tolkien wrote Eilenach is "probably an alien name, not Sindarin, not Númenórean, or Common speech." Perhaps it was pre-Númenórean.