Sindarin is the fictional language created by J.R.R. Tolkien that includes the word for friend, mellon.
In The Lord of the Rings, the inscription on the Doors of Durin uses the phrase “pedo mellon a minno,” meaning “speak, friend, and enter.” The word mellon is therefore a memorable example of Sindarin, the Elvish language most commonly spoken by Elves in Middle-earth during the Third Age.
Tolkien developed Sindarin with a sound and structure influenced especially by Welsh. He also constructed related historical forms to give the language the appearance of changing over time, rather than treating it as a collection of isolated invented words.
Quenya is another major Elvish language, associated with an older and more formal tradition. The inscription’s wording is Sindarin, even though the scene is often broadly described simply as an Elvish-language clue.