E. De Felice notes that this surname was formed from a nickname of varied motivation —among them, stoutness or obesity— derived from tondo (and locally tundo), an Italian word meaning "round", related to the surname Rotondo. He stresses that it is very frequent in the Salento area —that is, the southernmost zone of the Apulia region, in southern Italy.

F. Miranda offers a different etymological perspective: he considers that the surname derives from aphaeretic forms —that is, with the fall of the initial syllable— of the Latin cognomen Rotundus. He adds that in some cases it could be linked with Rotondi, the name of one of the confraternities documented in the Novara area in the 13th century. Miranda also specifies the geographical distribution of the surname: its presence is predominant in Apulia, with specific zones of lesser concentration in Sicily, Lombardy, Friuli-Venezia Giulia, Emilia-Romagna, Campania, Lazio and other regions. In Sicily it appears in several provinces, among them Syracuse —with a presence in Solarino, Lentini and Carlentini—, Agrigento —in Palma di Montechiaro, Sciacca and Agrigento itself—, Catania, Trapani —in Erice— and Enna —in Centuripe.

Both explanations are compatible in their semantic core: both the nickname tondo noted by De Felice and the aphaeresis of the Latin Rotundus indicated by Miranda refer to the concept of "round". The difference lies in the mechanism of formation proposed by each author.