The secret language of the Dwarves in J.R.R. Tolkien’s Middle-earth is Khuzdul.
Khuzdul is the language associated with the Dwarves, who traditionally kept it private and used other languages when communicating with outsiders. Tolkien gave it a distinctive sound and structure, with some inspiration from Semitic languages. Its secrecy contrasts with the more widely encountered Elvish languages in his legendarium.
The best-known Khuzdul battle cry is “Baruk Khazâd! Khazâd aimênu!” meaning “Axes of the Dwarves! The Dwarves are upon you!” The inscription on Balin’s tomb in Moria also includes Khuzdul names and forms, including Khuzdul and Moria-related terminology.
Khuzdul is often confused with Sindarin or Quenya, which are Elvish languages. Sindarin is associated especially with the Grey-elves, while Quenya is a formal language of the High Elves. Westron is the Common Speech used across much of The Lord of the Rings, not the private language of the Dwarves.