The authors agree that this surname derives from a term referring to the inhabitants of the Carnia, a mountainous area of northern Friuli-Venezia Giulia, in the province of Udine. E. Costantini specifies that it is a diminutive of the Friulian term Cjargnél, which designates the "inhabitant of the Carnia", and documents its presence in Gemona from at least 1575.

E. De Stefani broadens the historical context: the ethnic nickname is documented from the 13th century and alludes to the Carnian origin of those who received it. He notes that the Carnia was known for its skilled weavers, which is why in some areas, such as the Belluno area, the gentilic carniello came to acquire the meaning of "weaver". Over time, that form became a surname.

As for its distribution, Costantini places it mainly in Gemona and also records it in Osoppo, Udine, Tolmezzo, Villa Santina, Codroipo and other localities of Friuli. De Stefani describes it as spread throughout Friuli and the northeast of Italy, in the regions of Veneto, Friuli-Venezia Giulia and Trentino-Alto Adige, with special density in Gemona and presences in Enemonzo. He adds that the Germanised form Karnel is documented in southern Austria, in particular in Villach and Klagenfurt.