From Germanic

Means "nobleness, nobility", from the French form of the Germanic name Adalheidis, which was composed of adal "noble" and the suffix heit "kind, sort, type". It was borne in the 10th century by Saint Adelaide, the wife of the Holy Roman emperor Otto the Great.In Britain the parallel form Alice, derived via Old French, has historically been more common than Adelaide, though this form did gain some currency in the 19th century due to the popularity of the German-born wife of King William IV, for whom the city of Adelaide in Australia was named in 1836.