The surname presents independent origins in different regions of Italy. E. Rossoni notes that Sima would seem to be native of Tarvisio, and considers it an altered form derived from Simaz, a surname typical of San Leonardo in the Udine area. This in turn would derive from the Slavic name Simac, a Croatian form of the name Simone or Simeone. In some cases, Rossoni does not rule out that the origin is toponymic, from the locality of Simaz, in the Lusevera area, also in the Udine area. The variants Sime and Simec would likewise be forms derived from that same line.

V. Blunda, on the other hand, documents a branch of Sicilian origin and dialect character. According to this author, the surname comes from the word sima, with the meaning of "the highest point, summit," and as a surname could have originated in a microtoponym or in a nickname applied to one who lived in an elevated place.