The surname Toso belongs to a wide group of surnames of northern Italy formed from the base toso, a dialectal word very widespread in northern areas that continues the Latin tonsus ("cut, shorn"). In medieval Italy, this term acquired an appellative value with the meaning of "boy" or "young man", in allusion to the short haircut that distinguished children and adolescents. From that descriptive use, it early became fixed as a byname and later as a hereditary surname.

This interpretation is shared by E. De Felice, who includes Toso within the set of surnames derived from toso / tosi, very productive in the north and centre of Italy, and notes its semantic continuity from tonsus towards the idea of youth. Within this framework, Toso functions as the base form from which numerous patronymic, augmentative and diminutive derivatives develop.

From the geographical point of view, the surname has a strong historical implantation in the Triveneto and in Friuli, with a presence documented in areas such as the Carnia, the Udine area, the Pordenone area and bordering zones of Veneto. Studies on Friulian surnames highlight that the forms derived from toso spread widely in relation to the internal mobility and the seasonal migratory movements characteristic of the Alpine communities. In this context, Toso is configured as a surname of appellative-descriptive origin, not linked to trades or place names, but to a social characteristic common at the time of its formation.

To this same origin refer various variants and related surnames. Tosi is one of the most widespread forms in the north and centre of Italy, with the same meaning of "young man" or "boy", and constitutes a particularly productive base for the formation of other surnames. Toson, typical of Veneto and Friuli, incorporates the augmentative-patronymic suffix -on, frequent in the Venetan area, with the value of filiation or belonging to an ancestor called or nicknamed Toso.

For its part, Tosoni represents a plural patronymic form, in which the suffix -oni reinforces the idea of lineage or descent. Tosetto and Tosetti present a diminutive suffix (-etto / -etti), probably with an affectionate value or used to differentiate family branches within the same community. Along the same lines, Toselli incorporates the suffix -ello / -elli, with a likewise diminutive or familiar nuance, while Tosini responds to a pluralizing patronymic formation with the suffix -ini, frequent in northern Italy.

Finally, according to R. Brondolo, the origin in the Latin tonsus ("shaven") may have generated in some cases a secondary interpretation linked to the figure of the cleric, on account of the tonsure characteristic of the religious sphere. This reading does not exclude the main one —related to youth—, but reflects the semantic richness of the term in the medieval context.