E. Rossoni proposes several hypotheses on the origin of this surname. The first links it to the term rusca, with the meaning of "splinter or piece of wood." The second suggests a derivation from the Latin byname Roscius or Ruscius. The third connects it with the Latin cheruscus, linked to the name of the Germanic people of the Cherusci. Lastly, Rossoni notes a variant that relates the surname to the dialect term rüsca, "bark," used to tan hides, which would associate it with the trade of the tanner.

R. Brondolo leans directly towards this last hypothesis: the surname would come from the dialect rüsca, "husk, bark," a material necessary for the tanning of hides, and he therefore considers it linked to the trade of the tanner.

Rossoni further documents an early historical presence of the surname in the Como area: in 1175 Bernardo Rusca is recorded as governor of that city, and from the year 1300 the Ghibelline noble line of the Counts Rusca exercised the lordship over Como and the municipalities of Lake Como under Franchino Rusca.