E. Rossoni derives the surname from the medieval name of Germanic origin Gaidus, from which the name Guido would also derive. As an example of use in the Lombard period he cites the text: Rotecausus et Gaidus ducibus, cum multis Foroiulianorum consilio inito. Rossoni considers it peculiar to the Turin area.

V. Blunda presents it as a surname of Germanic origin derived from the personal name Gaidu, linked to the Lombard root gaid (dart, throwing weapon, light spear). He warns that the popular interpretation that associates it with the old Italian adjective gaio ("cheerful, festive") constitutes a crossed etymology, since that adjective derives from the Provençal gai, of distinct origin and without relation to the Germanic anthroponym. According to Blunda, as a surname it is preserved especially in Alpine zones of Piedmont and Lombardy, regions where Lombard anthroponymy left particularly dense traces until the modern period.