The fictional language spoken by the Dwarves in Tolkien’s legendarium is Khuzdul. Tolkien presented it as the secret language created for the Dwarves, who called themselves the Khazâd.
Khuzdul was not generally shared with outsiders. The Dwarves commonly used other languages when communicating with neighboring peoples, while preserving Khuzdul as an important marker of their identity and community.
Tolkien designed Khuzdul with a structure inspired partly by Semitic languages. Its vocabulary is limited in the published stories compared with Quenya or Sindarin, but names, battle cries, and inscriptions provide important examples. The word “Moria,” for instance, is an Elvish name, not the Dwarvish name for the underground realm.
Khuzdul is sometimes mistaken for the Black Speech of Mordor, but the two languages belong to different peoples and narrative traditions. Khuzdul is tied to Dwarven culture, whereas the Black Speech was devised for servants of Sauron.