Treebeard calls the Ents’ language Entish in Tolkien’s Middle-earth.
Entish is the language of the Ents, the ancient tree-like beings who guard parts of Middle-earth. Treebeard explains that Entish is extremely slow and elaborate, reflecting the Ents’ long lives and patient way of thinking. A single conversation can take far longer than speech among humans or hobbits.
In The Lord of the Rings, Merry and Pippin encounter Treebeard in Fangorn Forest. Their meeting helps bring the Ents into the conflict with Saruman, whose industrial destruction of the forest provokes the Ents’ attack on Isengard.
Entish is distinct from Elvish languages such as Quenya and Sindarin, and from Westron, the Common Speech used by many peoples. Tolkien also suggested that Entish was difficult for other peoples to learn or reproduce accurately.