Adelaide is the English form of the Germanic Adalheidis — composed of adal (noble) and heid (kind, sort). The same root also gives Alice, Adele, Adeline, and Heidi. Saint Adelaide of Italy (931-999) was a Holy Roman Empress; Queen Adelaide of Saxe-Meiningen (1792-1849) was the queen consort of King William IV.
Adelaide is the capital of South Australia, named after Queen Adelaide. The name has been continuously used in English but never enormously popular. Today it sits in the U.S. top 250 and is climbing fast.
Adelaide reduces to five — the number of noble motion.