What was the original name of Mirkwood in J.R.R. Tolkien’s legendarium?

Mirkwood was originally called Greenwood the Great in J.R.R. Tolkien’s legendarium.

Greenwood the Great was a vast forest in the northeastern part of Middle-earth. During the Third Age, the Necromancer Sauron established the fortress of Dol Guldur in the southern part of the forest. His influence caused the woodland to become dark and dangerous, leading to the name Mirkwood.

The forest is a major setting in The Hobbit. Bilbo and the Dwarves cross it on their journey to the Lonely Mountain, encountering giant spiders and the Elvenking’s halls. In The Lord of the Rings, Mirkwood remains an important realm associated with Thranduil and Legolas.

After Sauron’s defeat, the southern forest is cleansed and renamed Eryn Lasgalen, meaning Wood of Greenleaves. Thus, Greenwood, Mirkwood, and Eryn Lasgalen refer to different historical phases of the same forest.