The authors differ on the origin of this surname. E. Rossoni proposes two routes: a link with the place name Cassaro or with the trade of cassaio, that is, maker of boxes. Rossoni places the surname mainly in Sicily and also notes presence in the Turin area for the variant Cassarotto.

G. P. Holmes offers a different etymology and derives it from Arabic, with the meaning of "seller of mats". This proposal reflects the Arabic influence in Sicilian onomastics, product of the Islamic presence on the island during the Early Middle Ages.

V. Blunda proposes, on the other hand, a Greek origin, derived from the form Cassarás, belonging to the Byzantine onomastic repertoire transmitted to Sicily during the period of Greek presence. According to Blunda, the surname was fixed following the habitual pattern of the Greek forms ending in -as that became surnames in the regional onomastics of eastern Sicily.

The three hypotheses —Latin craft, Arabic and Greek— are not necessarily mutually exclusive, given that Sicily was the scene of successive cultural superimpositions that left their mark on its onomastics.