Mellon is the Sindarin word for “friend” on the Doors of Durin in J.R.R. Tolkien’s The Lord of the Rings.
The Doors of Durin stand at the western entrance to Moria, also called Khazad-dûm. Their inscription gives the instruction “Speak, friend, and enter,” but the wording is a linguistic puzzle: the speaker must say the Elvish word mellon, meaning “friend,” rather than offer a password in the usual sense. The doors then open.
The inscription was created by Celebrimbor, while the doors themselves were made during the friendship between the Elves of Eregion and the Dwarves of Moria. Gandalf initially struggles with the puzzle before recognizing that “friend” is the command. Mellon is Sindarin, one of Tolkien’s Elvish languages. It should not be confused with Elessar, Aragorn’s royal name, or Namárië, the title of Galadriel’s lament in Quenya.