The authors agree that the surname Maini —together with its variants Maino, Mainini, Mainino and Mainoldi— derives from the name of Lombard origin Mainold, linked to the Germanic root magin, which means "strength".

E. Rossoni notes that Maini is proper to Emilia-Romagna, while Mainini is decidedly Lombard, with a presence in the Milan and Como areas and a specific area in that of Reggio Emilia. Mainino, absolutely rare, would appear to be from the Varese area, and Mainoldi, also very scarce, would likewise be Lombard. Maino, by contrast, shows several cores: in the Bari area, in Trentino, in the Vicenza area, and in those of Milan and Como.

Rossoni documents the fixing as a surname through historical figures: the Milanese jurist and senator Iason Maynus (1435–1519), the legal advocate Orlando Mainoldi cited in judgements of the Bergamo area in the 16th century, and the notary Pietro Maino, active in the Vicenza area in that same century. It is further held that the surname Maino does not appear in documents of Milan until 1412, the year in which some of its bearers were proscribed.