E. De Stefani notes that this surname arose as an affectionate form of the Latin name Antonius, which in its dialectal variant took the forms Tonèl or Tunèl, interpretable as the result of combining the name Antonio with the diminutive suffix -ellus. The name Antonius was already Latin, of possible Etruscan origin, and its diffusion in Europe is due in good part to the figure of Saint Anthony of Padua. Over time, this affectionate form became a surname.

De Stefani documents the presence of the surname in Forni di Sotto, in the Carnia —a mountainous zone of northern Friuli, in the province of Udine—, at least from the 17th century. He also notes that at the end of the 15th century it is attested in the Tramonti di Sopra area, a locality historically linked to Forni di Sotto through the pass of Monte Rest.

F. De Laurentiis offers a convergent, though more concise, explanation: he considers that the surname derives from Tognoli, a dialectal form of Antonio.