According to E. De Felice and F. De Laurentiis, Avogadro is an occupational surname derived from the northern Italian dialect terms avogadro or avogaro, regional variants of avvocato (“lawyer”), particularly common in Veneto. In medieval Italy, however, the term had a broader meaning than the modern profession of lawyer and was also applied to high-ranking public officials, commercial magistrates, and municipal authorities.

De Felice and De Laurentiis explain that the surname likely originated as a professional designation identifying an individual who served in one of these important legal or administrative roles. Such officials could be responsible for commercial affairs, public administration, or the governance of local communities.

E. Rossoni agrees with this interpretation and emphasizes that avogadro referred not only to legal representatives but also to officials entrusted with significant administrative responsibilities. He notes that in the 13th century, noble families in the Brescia area charged with defending ecclesiastical property were known as Avogadri. He also documents the surname in Venice around 1400 and in Bergamo by 1470, demonstrating its long-standing presence in northern Italy.

Overall, Avogadro is an occupational surname derived from a medieval title associated with lawyers, administrators, and public officials, reflecting the important civic and legal functions held by the family's ancestors.