Sindarin is the Grey-elven language in J.R.R. Tolkien’s legendarium. Tolkien based much of its sound and historical development on Welsh, while Quenya, another major Elvish language, was strongly influenced by Finnish and Latin.
In the fictional history, Sindarin developed among the Sindar, or Grey Elves, in Middle-earth. It became a widely used Elvish language during the later First Age and was spoken by many Elves in Beleriand and later regions. Characters such as Legolas use Sindarin names and forms, although the books do not present every conversation as a language lesson.
Quenya and Sindarin are related within Tolkien’s constructed linguistic history, but they have different roles and sound patterns. Quenya is associated especially with the High Elves and retained a more formal or ceremonial status in many settings. Sindarin was generally the more commonly spoken Elvish language in Middle-earth during the Third Age.
Tolkien developed both languages over many years, revising their vocabulary and grammar repeatedly. They are therefore more than decorative word lists: each has a fictional history and relationship to other languages.