The authors agree that this surname derives from the medieval Latin feudal term vassus vassorum, which designated a vassal dependent not on the sovereign but on another vassal. The corresponding Italian form is valvassore or, in its Sicilian dialectal variant, vavassùri, with the sense of "baron" or "feudal knight".

V. Blunda specifies that the surname has roots in Sicily and that there it could have originated as a nickname applied to a person of feudal rank or linked to seigneurial service, a form introduced on the island during the Norman period. The base term vassus could be of Celtic origin, meaning "servant", and the surname is characteristic of the Bergamo area and the Lombard plain. The surname Vassalli is also mentioned as a kindred form, likewise present in that zone, which would reflect the feudal and Germanic influence in an Italy historically little feudalized.

The surname therefore presents independent stems of origin: one in the Bergamo area and Lombardy, and another in Sicily, arisen from the same medieval Latin etymon but in different regional traditions.