What was the name of the woodland later called Mirkwood in J.R.R. Tolkien’s Middle-earth?

The woodland later called Mirkwood was originally named Greenwood the Great.

Greenwood the Great was a vast forest east of the Misty Mountains. After the rise of the Necromancer, Sauron, at Dol Guldur, a growing shadow corrupted and enclosed the southern part of the forest. Its name consequently changed to Mirkwood.

The forest is an important setting in The Hobbit. Bilbo and the dwarves cross it on their journey to Erebor, encountering giant spiders and the Elvenking’s halls. In The Lord of the Rings, Mirkwood remains a major realm of the Woodland Elves under Thranduil.

Mirkwood is not the same as Fangorn, Lothlórien, or the Old Forest. Those woods have different locations, histories, and inhabitants. The name change also reflects Tolkien’s recurring pattern of landscapes being transformed by evil and later renewed.