Short form of Alessandra, the Italian form of Alexandra. A major influence in establishing this as a common given name in the English-speaking world was George Meredith's novel Sandra Belloni (1886), originally published as Emilia in England (1864); the heroine, Emilia Sandra Belloni, is a beautiful, passionate young singer.
English and Scottish: from a Celtic personal name of great antiquity and obscurity. In England the personal name is now usually spelled Alan, the surname Allen; in Scotland the surname is more often Allan. Various suggestions have been put forward regarding its origin; the most plausible is that it originally meant ‘little rock’. Compare Gaelic ailín, diminutive of ail ‘rock’. The present-day frequency of the surname Allen in England and Ireland is partly accounted for by the popularity of the personal name among Breton followers of William the Conqueror, by whom it was imported first to Britain and then to Ireland. St. Alan(us) was a 5th-century bishop of Quimper, who was a cult figure in medieval Brittany. Another St. Al(l)an was a Cornish or Breton saint of the 6th century, to whom a church in Cornwall is dedicated.