From Tolkien Gateway

Eilenaer was a tall hill or mountain with its feet shrouded by woodland, Eilenaer was in many ways similar to Eilenach, which stood far to the east in the Drúadan Forest, and indeed these two ancient names appear to be related in meaning. While Eilenach kept its old name, Eilenaer was renamed when it became the site of Elendil's Tomb. In Gondor after that time it was known by the Elvish title Amon Anwar, 'Hill of Awe'. When the Rohirrim came to settle in Rohan, long afterwards, they gave it another name in their own tongue - Halifirien, the 'Holy Mountain' on the borders of their realm.[1]


Eilenaer was a name of pre-Númenórean origin, evidently related to Eilenach.