J.R.R. Tolkien described the Entwives as the Ents’ missing partners.
Entwives are the female counterparts of the Ents, the tree-like shepherds of Middle-earth. The Ents and Entwives once lived together, but they developed different ways of life. The Entwives preferred gardens, agriculture, and the cultivation of ordered lands, while the Ents remained closely associated with forests and wild growth.
The Entwives’ gardens were destroyed during the wars of the Second Age, and the Entwives disappeared. In The Lord of the Rings, Treebeard tells the hobbits that the Ents have searched for them without success. The text leaves their ultimate fate unresolved, although characters hope that some may have survived.
They are not simply another name for female Ents appearing in the story, because Tolkien presents them as a vanished people whose absence shapes the Ents’ history. The Entwives’ disappearance also helps explain why the Ents are dying out and why there are no young Ents.