From Latin iūlius, through a process of dissimilation; compare also the obsolete regional variant form giuglio. Alternatively, derived from a Vulgar Latin root *lūlius, along with other Italo-Romance and Rhaeto-Romance cognates; compare Corsican lugliu, Neapolitan lùglio, Sicilian lugghiu, Venetan lujo, Romansch lügl, Friulian Lui, Ladin lugio, Ligurian lûggio, Emilian and Romagnol lój, Lombard luj. Gallo-Roman town name Juliobona (nowadays in Normandy, France) evolved into its modern French name Lillebonne following the same process.
Doublet of Giulio.