Sindarin is the Elvish language J.R.R. Tolkien developed with strong Welsh-inspired phonology.
Sindarin is one of Tolkien’s major constructed languages and is associated primarily with the Sindar, or Grey Elves. In the imagined history of Middle-earth, it became a widely used Elvish language in Beleriand and later in parts of Middle-earth.
Tolkien based important aspects of Sindarin’s sound and structure on Welsh. He was a professional philologist and designed his languages historically, giving them related forms, sound changes, and evolving vocabularies rather than treating them as collections of isolated words.
Sindarin is often confused with Quenya, another major Elvish language. Quenya is associated especially with the High Elves and was influenced in part by Finnish. Tolkien’s fictional languages are presented through names, phrases, and scattered texts, so neither language has the complete everyday vocabulary of a natural modern language.