From the word "tedesco" = someone from Germany.

The authors agree that this surname derives from the demonym tedesco, meaning "belonging to the German populations, of Germany", and that it is diffused throughout the Italian peninsula.

E. De Felice offers the most detailed analysis. He notes that the term is documented in Italy from the 12th century in Latinized forms such as Teudiskus, Todescus, Todischus, Todeschinus, Tediscus, Taudesca and Thoescanus. De Felice traces its etymon to the Germanic *theudisk or *theodisk —from which comes the German deutsch—, formed by *theuda-, "people" (as an ethnic community and territory), plus the ethnic suffix *-isk, within a predominantly Frankish tradition.

De Felice also distinguishes regional variants: the northern forms Todesco and Toesco —with Romance lenition of the -d-—, and the southern Todisco and Tudisco. In the north-east, especially in Veneto, forms such as Todesca, Todeschin, Todescan and Todescato are recorded. The variant Tedisco appears in Friuli-Venezia Giulia, while Tudisco is very frequent in Sicily and Calabria.

E. Rossoni adds that the demonym was applied both to those who were native of Germany and to those who presented physical or behavioural characteristics associated with that origin.