E. Rossoni notes that this surname derives from an apocopated dialectal form of the name Costanzo, probably borne by the founder of the family. He further indicates that Stanzu is an altered variant of Stanzù, a form he considers typically Sicilian and which is documented in Leonforte, in the Enna area, and in Capizzi, in the Messina area, while Stanzu is practically unique.

F. Miranda agrees that the surname derives from an aphaeretic dialectal form of Costanzo, the personal name of the first bearer, and adds that Costanzo has its roots in the Latin term constantius, meaning "firm, tenacious, persevering". Miranda offers a more detailed geographical description: the surname appears scattered across some twenty municipalities, with its main nucleus in Sicily —specifically in the Enna area (Leonforte, Cerami, Troina, Gagliano Castelferrato, Enna, Agira, Centuripe, Regalbuto, Valguarnera Caropepe and Aidone), in the Catania area and in the Messina area (Capizzi)— and with an additional presence in Piedmont, Lombardy and Veneto.