Mellon is the word that appears as the password in J.R.R. Tolkien’s inscription over the Doors of Durin.
The Doors of Durin are the western entrance to Moria, also called Khazad-dûm. The inscription is written in Sindarin, using Tengwar script, and includes an instruction meaning “speak, friend, and enter.” The needed word is Mellon, the Sindarin word for “friend.”
The Fellowship initially struggles because the inscription is interpreted as a command to say a password rather than as a simple instruction. Gandalf eventually realizes that the answer is not a secret name but the word friend itself. When he speaks Mellon, the doors open.
The scene demonstrates Tolkien’s interest in the relationship between language, writing systems, and history. The inscription was made by Celebrimbor, while the doors were created by the Dwarves of Moria. This is why the entrance combines Elvish writing and language with a Dwarven architectural setting.