The surname Blasi and its variants —such as Blasio and Blaso— have an anthroponymic origin of Latin root. According to E. Rossoni, they derive from the name Blasus or from the praenomen Blaesus, meaning "stammerer" or "one who lisps". This type of name, originally a nickname linked to physical or speech characteristics, was later transmitted as a personal name and finally as a surname.

From the point of view of diffusion, E. Rossoni notes that Blasi is present throughout Italy, although it predominates in the centre-south; Blasio is more typical of Campania, especially in the Naples and Salerno areas, while Blaso is very rare, with clusters in areas such as Benevento and Bari. These variants reflect regional adaptations of the same common origin.

For his part, F. De Laurentiis confirms this etymology, indicating that the surname is based on the Latin adjective blaesus, meaning "lisping" or "who speaks with difficulty". Taken together, both interpretations agree in pointing to an origin linked to a speech trait, which passed from nickname to personal name and then to hereditary surname within different Italian regions.

On the other hand, V. Blunda considers that it is a Sicilian surname of dialectal origin, formed from a personal name. It derives from the dialectal word bràsi, the Sicilian form of the proper name Biagio (Saint Blaise). The cult of the Armenian saint, a 4th-century martyr invoked against throat ailments, spread widely in Sicily through the popular confraternities and the celebration of his feast on 3 February, with the blessing of throats and loaves in the parishes. The name became popular as an anthroponym and gave rise to the hereditary surname.