The authors differ on the etymology of this surname. E. Rossoni proposes two hypotheses. The main one derives the surname from contractions of the Germanic name Ishard, composed of is or isan ("iron") and hard ("hard"), meaning "hard as iron", Latinized as Izardus. As an alternative hypothesis, Rossoni suggests that in some cases it could derive from names of localities characterised by the presence of oaks (izza) or of the snail (izzu) in Sicilian. Geographically, Rossoni places the surname in the Ragusa area —specifically in Vittoria— and in the Caltanissetta area, in particular in Gela.

V. Blunda, on the other hand, proposes a Greek origin: it would derive from decsiàs, a term that designates the right hand or manual skill. According to this hypothesis, the surname would have arisen as a nickname applied to an ancestor for his physical dexterity or his dominant handedness, following the habitual patterns of the Sicilian nicknames of Greek origin derived from bodily traits.