The authors agree that this surname derives from the personal name Giglio (and its feminine form Giglia), belonging to the group of names formed from flowers with symbolic value: the lily, a symbol of candour and purity.

E. De Felice notes that the forms with initial z- reflect the adaptation proper to Veneto, where giglio takes dialect variants such as zégio, zéio and zéi. He further indicates that the variants Giglia, De Giglio, Gigliano and Gigliuto are proper to southern Italy, while the forms with z- are specific to Veneto.

E. Rossoni adds that Giglia could also derive from the ancient place name Giglius, a Roman territory in Libya, and that Gigli could likewise be linked to one of the numerous Italian place names containing the term giglio. According to Rossoni, Giglia originates in the Agrigento area; Gigli is concentrated in central Italy, especially in the Marche and Tuscany; and Giglio is widespread in the south, with a greater presence in the Calabria area and in Sicily. Rossoni further documents that around 1500 an Aloigi Giglio is recorded, a native of Cirò, in the Calabria area, identified as the principal architect of the Gregorian calendar.