Pet form of Adelaide or Adeline, from Germanic 'adal' meaning 'noble.'
Addie is an English pet form that grew out of a whole family of names: Adelaide, Adeline, Adele, Addison, and sometimes even Adam or Adrian. In practice, though, it has been most strongly associated with the Adelaide and Adeline branch, both of which trace back to Germanic elements meaning "noble" or "nobility." That gives Addie a charming double life.
On the surface it sounds playful, clipped, and affectionate; underneath, it inherits the grandeur of older formal names carried by saints, queens, and 19th-century heroines. It is a nickname with aristocratic ancestry. By the late 19th and early 20th centuries, Addie was common enough in the English-speaking world to stand on its own, especially in the United States, where many nickname-style names became independent given names.
It later faded as fashions shifted toward more formal spellings, then returned as part of the modern revival of vintage diminutives. Historical bearers such as Addie L. Ballou, the suffragist and writer, or Addie Aylestock, the pioneering minister, give the name substance beyond its sweetness.
It also appears in American memory through tragic and civil-rights-era associations such as Addie Mae Collins. Today Addie feels bright, familiar, and old-fashioned in the best way: informal yet rooted, friendly yet substantial. It has the sound of a porch nickname and the pedigree of a much older house.