J.R.R. Tolkien called the language spoken by the Ents in The Lord of the Rings Entish.
Entish is described as extremely slow, lengthy, and difficult for other peoples to learn. Treebeard explains that Ents do not rush into speech because their language reflects their patient, deliberate nature. In the story, Merry and Pippin spend days waiting while the Ents discuss whether to take action against Saruman.
Tolkien gives relatively little direct Entish vocabulary compared with languages such as Sindarin or Quenya. This is deliberate: the language is portrayed as almost inseparable from the Ents’ long memories and careful thought. Entish should not be confused with Westron, the commonly spoken language of many characters, or with Black Speech, created for servants of Sauron.