Hírilorn was a beech-tree and the tallest and greatest of all the trees in the Forest of Neldoreth in the northern kingdom of Doriath.

This magnificent tree that was not far from the gates of Menegroth had three trunks equally round and smooth; the only branches that grew from them was a great height above the ground.

King Thingol bade Lúthien to dwell in a house that was built in between the trunks of Hírilorn so that she could not escape and venture into danger beyond the Hidden Kingdom.

Lúthien, however, escaped from Hírilorn by means of enchantment and hurried to the aid of Beren Erchamion. For this Hírilorn received the name 'Tree of the Lady'.
Encyclopedia entry originally written by Arien