The sources differ both on the etymology and on the geographical origin of this surname.

E. De Stefani places its origin in Forni di Sopra, a locality of the Carnia —a mountainous zone of the north of Friuli, in the province of Udine—, where it is documented from the end of the 15th century. According to De Stefani, the surname derives from Jacomìs, a Friulian affectionate form of Jacomo, itself coming from the Latin Jacobus. In everyday oral use, the form Jacomìs would have lost its initial syllable, giving rise to Comis, which over time became a surname.

V. Blunda, on the other hand, relates it to the Greek comes, meaning "count", and links its origin to Sicily. For Blunda, the term designated a noble title peculiar to the Byzantine administrative apparatus, and the surname would have arisen as a crystallisation of the office held by an ancestor. The author also notes its relation with the surnames Comità and Còmito, recorded in the immediately adjacent entries of his work and derived from the same root.

Both proposals are etymologically incompatible and correspond to regions unrelated to each other, which suggests that the surname presents independent clusters of origin (ceppi) arisen in different regions without direct relation between them.