What name did J.R.R. Tolkien give the evil language used for the Ring inscription?

J.R.R. Tolkien called the evil language used for the Ring inscription the Black Speech of Mordor.

Sauron devised the Black Speech during the Second Age to serve as a common language for the servants of Mordor. The best-known surviving example is the inscription on the One Ring: “One Ring to rule them all, One Ring to find them,” followed by the lines describing binding and darkness. The inscription is written in Tengwar script but uses the Black Speech language.

This distinction is important because script and language are not the same thing. Tengwar is a writing system, while the Black Speech is the language represented by the Ring’s inscription. Tolkien created only a limited amount of Black Speech compared with languages such as Quenya and Sindarin.

Readers sometimes identify the inscription as Elvish because its lettering resembles Elvish writing. In Tolkien’s story, however, the words are a spell of Sauron’s language, and the script was used because the Ring’s letters were formed in a style associated with the Elves.