E. De Stefani links this surname with the dialectal verb tonsare ("to crop, to cut the hair"), noting that it was originally a frequent nickname in Friulian communities to refer to one who wore their hair short. Over time, that denomination became a surname. De Stefani adds that in northern Italy —especially in Lombardy and Veneto— there is also the word toso/a ("boy/girl"), which goes back to the same root, since young people used to wear their hair short, and from that extended meaning various related surnames arose.

E. Rossoni agrees in deriving the surname from dialectal nicknames linked to the term toso ("boy, beardless"), though in hypocoristic or augmentative forms, and also notes the possibility of a toponymic origin from Prato Tosone, in Friuli. Rossoni places the form Toson mainly in the Padua area, while Tosone would have a Friulian stem and another in the Abruzzo region. The form Tosoni is documented in the Rome and Rieti area, in the Brescia, Verona, Mantua and Cremona area, in Friuli, in the Siena area and in the area between Macerata and the Piceno.

De Stefani provides more detail on the Friulian distribution: the forms Toson are recorded in localities of the Carnia —a mountainous zone of northern Friuli, in the province of Udine— such as Quinis, Enemonzo, Preone, Socchieve and Verzegnis, as well as in Campoformido. The variants Tosoni and Tosone appear in the Pordenone area, and the form Tosolini is especially dense in the Udine area.