E. Rossoni notes that Carlessi is a very scarce surname, characteristic of the Bergamo area, while its variant Carlesso, somewhat less scarce, is concentrated in the area between Vicenza and Treviso. Both forms would be of patronymic origin, derived with the suffixes -ssi and -sso from a dialectal modification of the name Carlo, with the sense of "son of someone called Carlo". The first documentations of its transformation into a surname go back to the 17th century in the Treviso area.

For its part, the surname is considered to be of anthroponymic origin and to derive from the Germanic name Karl, meaning "free man", with presence in the plain of Lombardy.