E. Rossoni, F. Miranda and F. De Laurentiis agree that Giannino derives from the personal name Gianni, a familiar and hypocoristic form of Giovanni, one of the most widespread names in Italian tradition.

E. Rossoni considers it a rare surname of Sicilian origin, particularly associated with Catenanuova in the province of Enna and with parts of the Catania area. He suggests that it is a relatively recent surname that developed from a dialectal form of the name Giovanni. Rossoni further proposes that the surname may originally have identified a man named Gianni who came from Noto, in the province of Syracuse.

F. Miranda supports this interpretation and provides a philological explanation based on the studies of Rohlfs and Caracausi. According to this hypothesis, the surname developed through the fusion of a personal name and a demonym: Gianni-nòto (“Gianni from Noto”) gradually evolved into Gianninò, from which the modern surname emerged. Miranda notes that the surname is also found in other Sicilian localities, including Lentini in the Syracuse area and Ramacca, Castel di Judica, Sant'Agata Li Battiati and Viagrande in the province of Catania.

Outside Sicily, Miranda records smaller branches in Lombardy, Tuscany, Piedmont, Lazio, the Marche, Veneto and Trentino-Alto Adige. F. De Laurentiis likewise identifies the surname as a direct derivative of the personal name Gianni.

Overall, Giannino is a surname of anthroponymic origin, derived from a familiar form of Giovanni, and may in some cases preserve the memory of an ancestor identified by both his given name and his place of origin.