The authors agree in pointing to a Greek root as one of the possible etymologies of the surname. G. Rohlfs considers it of Greco-Byzantine origin and derives it from the Calabrian dialect gullu ("hornless"), itself from the ancient Greek κόλος ("truncated, docked"). He notes its presence throughout Calabria, in the Neapolitan and Sicilian spheres, and gives as a variant the form Gully, further referring to the related surnames Logullo and Gullì.

F. Miranda takes up this same Calabrian dialect hypothesis —gullu, from the Greek goylòs—, linking it to a sense referring to the physical integrity of the first bearer of the surname, but presents it as one possibility among several. The other hypotheses Miranda handles point to the Latin cognomen Gullus, to the Norman name Gulian, or to an aphaeresis —that is, the loss of the initial syllable— of Latin names such as Agulus, Figulus or Regulus.

As for geographical distribution, Miranda describes a broad presence across different regions of Italy, with areas of greatest concentration in Sicily and Lazio, and offshoots in Lombardy, Piedmont, Liguria, Tuscany, Emilia-Romagna and Campania. In Sicily, the surname appears in almost every province, with a particular presence in the Messina, Palermo, Catania and Trapani areas.