The authors agree that the surname was formed from the Germanic personal name Aldo or Alda, derived from the root alda ("old, aged, wise through age").

E. De Felice specifies that the name was already Lombard, but was spread in Italy by the Franks and later reinforced by contacts with France and with French culture and literature. He recalls that Alda la Bella, in the Carolingian poems, is the betrothed of Roland.

De Felice adds that the Germanic base alda- means "old" (German alt, English old) but also "wise, expert", and that it is frequently a hypocoristic of compound names that have this base as their first element, such as Aldeprando.

De Felice notes that the surname is widespread in north-central-western Italy, in Tuscany and in the peninsular south, and that the Aud- forms are peculiar to Piedmont and the Naples area.

V. Blunda, for the Sicilian variant, derives it from the Germanic personal name Alda. He notes that the root alda is one of the most productive elements of Lombard anthroponymy, present in numerous compounds where it is associated with virtues such as prudence, experience and political authority. He adds that as an autonomous name it was preserved in many Italian regions, reaching Sicily with the medieval Germanic waves.