Variant of Adeline, from Germanic 'adal' meaning 'noble,' popularized through French medieval usage.
Adelaine is an elegant variant spelling of Adelaide, itself derived from the Old High German Adalheidis, a compound of adal, meaning 'noble,' and heid, meaning 'kind' or 'type'—yielding the full sense of 'of noble kind.' The name traveled with the Normans into England and across Europe, becoming one of the defining names of medieval aristocracy. Adelaide of Italy, wife of Holy Roman Emperor Otto I in the 10th century, was so revered that she was later canonized as a saint.
The Adelaide-Adelaine family enjoyed enormous prestige in the 19th century. Queen Adelaide of Saxe-Meiningen, wife of King William IV of Great Britain, lent the name royal luster, and the Australian city of Adelaide was named in her honor in 1836. The variant spelling Adelaine adds a graceful extra syllable to the eye, giving it a slightly more flowing, poetic quality that appealed to Victorian parents who favored ornamentation in naming as in architecture.
In the current revival of Edwardian and Victorian names, Adelaine is ripe for rediscovery. It sits adjacent to the popular Adelaide but a step apart—more unexpected, more lyrical. The name carries its full weight of noble etymology without feeling stuffy, and its four syllables provide natural nickname territory in Addie, Laine, or Della. It is a name that rewards attention.