(Middle Ages) the bride of the king of Cornwall who (according to legend) fell in love with the king's nephew (Tristan) after they mistakenly drank a love potion that left them eternally in love with each other

Iseult (alternatively Isolde, Yseult, Isode, Isoude, Isotta, etc.) is the name of several characters in the Arthurian story of Tristan and Iseult. The most prominent is Iseult of Ireland, wife of Mark of Cornwall and adulterous lover of Sir Tristan. Her mother, the Queen of Ireland, is also named Iseult.