The name suffix -vain appears in this and other Arthurian names such as Yvain and Agravain.
The Cornish form of this name, Jennifer, has become popular in the English-speaking world.
According to tales first recorded in Old French in the 12th century, Yseut or Ysolt was an Irish princess betrothed to King Mark of Cornwall. After accidentally drinking a love potion, she became the lover of his nephew Tristan. Their tragic story, which was set in the Arthurian world, was popular during the Middle Ages and the name became relatively common in England at that time. It was rare by the 19th century, though some interest was generated by Richard Wagner's opera Tristan und Isolde (1865).
In Shaivism, a Hindu denomination, he is regarded as the supreme god. The other major sect, Vaishnavism, views Vishnu and his avatars as supreme.