The authors agree that this surname derives from the term that designates the fennel. R. Brondolo notes that it comes from the forms of the old Piedmontese fenügl and fenùi, meaning "fennel", and indicates that the surname was linked to families related to that cultivation. Other sources consulted by Surnames in Italy broaden this etymology and trace it back to the Vulgar or medieval dialectal Latin finocchio, noting that the surnames of this family could have originated in place names associated with places where fennel grew, in trades linked to its harvesting or sale, or as figurative bynames that over time became hereditary surnames. In Piedmontese dialect, the form fënu, derived from the old fënùl, was Italianized as Fenoglio.

The first historical documentations: in 1160 the form Feniculus appears in Genoa; in 1182, in Bari, Finoculus; in 1260, in Florence, Finocchius; and in 1363, in Turin, Fenoglus. Geographically, Fenoglio is peculiar to Piedmont, with greater concentration in the provinces of Turin and Cuneo. The variant Fenocchio appears also in Liguria, in the Savona area, with presence in the Cremona and Brescia area. In Sicily, the form Finocchiaro is especially frequent in the centre and the east of the island.