The authors agree that this surname derives from the Latin feminine personal name Arethusa, of Greek origin. E. Rossoni notes that the name corresponds to a character of Greek mythology, daughter of Nereus and Doris, and that in Late Latin times it was also used in the masculine as Arethusus. Rossoni also recalls the martyr Mark Arethusius, who during the reign of the emperor Julian the Apostate gave his life rather than support the reconstruction of a pagan temple.

V. Blunda specifies that the Greek etymon is Arèthousa and highlights its hydronymic dimension: the name corresponds also to the famous spring of Syracuse, which links the surname to Sicilian onomastics of Byzantine tradition. For Blunda, the Italian form of the surname results from the Italianised spelling of the name transmitted along the family line.

As for its geographical distribution, Rossoni indicates that the variant Aretusa is practically unique, while Aretusi appears sporadically in central-northern Italy, with a specific presence in Abruzzo, in localities of the Pescara and Teramo areas. The variant Aretuso records a small cluster in Ospedaletti, in the Imperia area. Blunda, for his part, places the surname in Sicily.