The authors agree that this surname derives from a name of good omen, related to the wish that the birth of a child would inaugurate a happy year. E. De Stefani notes that the nickname Bonan(n)us was frequent in central-northern Italy during the late Middle Ages, and that in some cases names of this type were shortened, giving rise to the surname Bon. He also proposes a parallel with the southern German surname Gutjahr, equivalent to the term Neujahr ("new year"). He also suggests that it could have been attributed to children born in the Christmas period, when the old year ended and the new one began.

E. Rossoni specifies that all the surnames of this group would derive from the name of good omen Bonusannus, and documents its presence from 1130 in Pisa, in the 14th century in Cividale del Friuli, and in the 17th century in Sicily and in Paganica, in the L'Aquila area. Rossoni indicates that Bonanni is very widespread in central Italy, with presence also in the Florence area, in central-eastern Liguria and in the Udine area, while the variant Buonanno is peculiar to Campania, in the Caserta, Naples and Benevento areas.

De Stefani adds that the surname has notable presence in Sicily and in the Carnia, a mountainous area of northern Friuli-Venezia Giulia, especially in Raveo and Tolmezzo, with documentation from the mid-16th century.