The surname Massolo is closely related to the surname Mazza and its derivatives. In particular, it comes from the form Mazzolo, one of the denominal surnames formed from mazza ("staff, mace"). In time, in various regions of northern Italy —above all in Piedmontese and Lombard areas— a characteristic phonetic change took place: the double -zz- evolved into -ss-, giving rise to variants such as Massolo.

Phonetic changes and the shift from -zz- to -ss-

In some regions of northern Italy, especially in Piedmontese and Lombard areas, the shift from -zz- to -ss- is recorded in surnames. This phonetic development can be clearly observed in the historical documentation. In the province of Alessandria, for example, the surname Massolo is very rare but typically local. In the course of genealogical research in the civil and ecclesiastical registers of the comune of Alessandria, it was established that the surname was originally written Mazzolo, and that only from the creation of the civil register in 1866 does it begin to appear as Massolo.

In the older parish documents, especially between the years 1700 and 1850, intermediate forms such as Mazzollis and Mazolis appear, which demonstrates the strong influence of the local dialects and the lack of orthographic standardization in earlier periods. The present-day form Massolo is therefore a phonetic development, reinforced by modern administrative usage.

Forms with a single S

Masola, very rare, would appear to originate in the Padua area. Masoli, likewise uncommon, would seem more typical of the regions of Emilia and Romagna. Masolini, less rare, would have one line in the Valtellina, one in the Udine area —where Masolino is also found— and another between Bologna and Florence. Masolo should be native to the Vicenza area.

According to E. Rossoni, all these surnames would derive from shortened forms (by aphaeresis) of diminutives of the name Tommaso.