The surname Zago is interpreted, according to the main scholars, from an origin linked to nicknames of occupational character and, in some cases, also to toponymic references. E. De Felice notes that it derives from the regional appellative zago, diffused in areas such as Veneto, Trentino, Brescia and Bergamo, meaning "deacon". This term comes from the Latin diaconus, in turn an adaptation of the Greek diákonos, and was used to designate ecclesiastical functions such as those of deacon, sacristan or altar boy. In addition, in certain dialectal contexts, the word acquired a figurative sense, being able to mean also "simpleton" or "boor".

Along the same lines, F. De Laurentiis confirms this origin, highlighting that the surname is diffused with medium frequency in the regions of the Venezie, as well as in Emilia-Romagna and eastern Lombardy. He reaffirms that it is a nickname derived from the term zago in its ecclesiastical sense, though he also recognises its figurative use in some zones. Likewise, he does not rule out that in certain cases the surname may be linked to a minor place name called Zago (in the Padua area), which would introduce a possible variant of geographical origin.