E. Rossoni derives this surname from a nickname originating in the Sardinian word aresu, with the meanings of "wild", "savage", "untamed" and "intrepid". He locates its presence in Sardinia, especially in the Cagliari area and the lower Nuoro area. Rossoni also notes possible alternative derivations: from the Latin root are ("dry", "arid"), from the Greek araiós ("rare"), or from the Sardinian verb resài ("to pray", "to invoke"), which would give the meaning of "invoked" or "longed-for".

V. Blunda, on the other hand, proposes for a Sicilian variant of the surname a different etymology: the derivation from the Greek personal name Arèthas, preserved through Byzantine transmission in southern Italy. According to Blunda, the Italianised spelling resolved the Greek th as s, giving rise to the current form via the original personal name.

Both proposals point to independent origins: an appellative Sardinian root in Sardinia, and a personal name of Greek-Byzantine origin in Sicily, which suggests that the surname presents independent stocks of origin (ceppi) arisen in different regions without direct relation to each other.