E. De Stefani notes that this surname is Friulian microtoponymic, derived from the dialectal forms Cjasasola or Cjasesole, attested in several areas of Friuli —among them Chiusaforte and Spilimbergo—, which designated a house or group of houses situated in a place apart from the inhabited nucleus of the village. Documented from the beginning of the 18th century in Raveo, in the Carnia, over time it became a surname. Today it is concentrated in Latisana, Ronchis, Palazzolo dello Stella and Muzzana del Turgnano, in the Bassa Friulana, as well as in Maiano, a locality of the province of Udine that has a homonymous hamlet that reinforces the toponymic motivation.

E. Rossoni confirms that the surname is typical of the Udine area and links it specifically to the place names Casasola di Frisanco, in the Pordenone area, or Casasola di Maiano, in the Udine area. Rossoni also extends the analysis to the variants: Casasole, characteristic of Orvieto and its surroundings, would derive from the union of the terms casa and sole ("sun"), in reference to a place name or to the place of residence of the founder of the lineage; and Casasoli, of almost testimonial presence, would probably be the result of transcription errors of Casasole.