Abyssal

Abyssal is the tongue spoken by the Old Ones and their cultists. Spoken in strange and alien syllables, legends claim that all who learn the full language eventually go mad from their knowledge. Few if any books are written in the Abyssal alphabet, and those that are, are kept out of sight of prying eyes, in deep vaults and hidden wings of ancient libraries. It is said to be understood by some variations of demons and devils too, likely to be in the service of the Old Ones.