The surname Amelio has an anthroponymic origin and derives from the personal name Amèlio (and its feminine Amèlia), a continuation of the Late Latin nomen Amelius. This name spread in Italy during the Late Middle Ages, partly thanks to the popularity of the character Amelio, one of the protagonists of the French Carolingian poem Amis et Amiles, well known in the Italian sphere.

Both E. De Felice and A. Bongioanni agree on this interpretation and also highlight the influence of the cult of Saint Amelio of Mortara, venerated as patron of Mortara, which contributed to the permanence and diffusion of the name.

From this base, a broad family of regional variants developed. Bongioanni notes Ligurian and Piedmontese forms such as Amelio, Amerio, Ameglio, Venetian forms such as Damerini and the Lombard variant Milesi, considered a contraction of Amilési. These differences reflect phonetic and dialectal processes peculiar to each region.

As for its diffusion, the surname Amelio shows a moderate presence in southern Italy, while many of its variants are concentrated in the northwest, which reveals a geographical expansion from a single name of medieval origin.

V. Blunda holds: a Sicilian surname of Germanic origin, derived from the personal name Amal, a patronymic root linked to the dynasty of the Amali, the royal house of the Ostrogoths to which Theodoric the Great (454–526) belonged. The dynastic name spread widely in medieval Italian onomastics as a sign of prestige. The ending -elio is the result of the adaptation to the morphological system of Italian, with the diminutive suffix applied to the Germanic base.