Isolde is from the Old High German Iswalda — īs (ice) + walt (rule). *The Irish princess heroine of the medieval romance Tristan and Isolde — betrothed to her uncle King Mark of Cornwall, but drinking a magic love potion with the knight Tristan en route to her wedding, she and Tristan fall into a hopeless and adulterous love that ends in their deaths. One of the foundational stories of European romance, with Arthurian connections — Tristan's roundtable knighthood appears in Malory. Wagner's opera Tristan und Isolde (1865) reinvented Western music* with its dissonant Tristan chord — among the most influential pieces of the 19th century.
Subject of Joseph Bédier's The Romance of Tristan and Iseult (1900) and Wagner's opera.
Isolde does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Isolde reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.