Mellon is the Elvish word for “friend” used to open the Doors of Durin in J.R.R. Tolkien’s Moria.
The Doors of Durin stand at the western entrance to Moria, beside the lake known as the Mirrormere. Their inscription says, in part, “Speak, friend, and enter.” Gandalf first interprets this as a command to say a password, but later realizes that the instruction means to speak the word “friend,” or mellon in Sindarin.
The scene highlights Tolkien’s interest in language and word history. Mellon is Sindarin, one of Tolkien’s Elvish languages, rather than Quenya, another major Elvish language. The Doors were made during the friendship between the Dwarves of Khazad-dûm and the Elves of Eregion.