E. De Felice, E. Rossoni, V. Blunda and N. Bergamo agree that the surname derives from the given name Achille (Achilles), of Greek origin.

De Felice specifies that it is the surname-formation of the name Achille —the Homeric hero, in Latin Achilles, an adaptation of the Greek Achil(l)éus—, which in Italy had limited diffusion in the Late Middle Ages through Byzantine influence. In Genoa it is attested, in medieval Latin notarial deeds of the 12th century, as Achilles and Achileus. He adds that it became more frequent only in the humanist and Renaissance period, with the recovery and new prestige of Greek and Latin culture and literature.

De Felice notes that it is spread mainly in Lombardy, Liguria and Emilia, with peaks in Milan and, for the altered forms, in Bologna.

Rossoni agrees that the surname derives from the given name Achille, probably borne by the founder of the lineage.

Blunda, for the Sicilian variant, derives it from the Greek etymon Achillèys ("Achilles"), in reference to the protagonist of Homer's Iliad, son of the nereid Thetis and of King Peleus, a symbol of warrior valour and human fragility. He notes that the name was preserved in Sicilian onomastics over the centuries as a reflection of the survival of Greek culture on the island, colonised from the 8th century BC within the framework of Magna Graecia.

Bergamo records it as a surname of Greek origin, taken from the given name.

The surnames Achille, Achilleo, Achilla, Achilli, Achillini, Dacchille, D'acchille, Dachille and D'achille are considered patronymics —derived from the father's name—, in this case Achille (Achilles), a name of Greek origin meaning "dark".

It is suggested that the patronymic could derive from the cult of Saint Nereus and Saint Achilleus, two Roman soldiers who converted to Christianity and were put to death in Rome, probably during the persecution of Diocletian, and are venerated as martyr saints by the Catholic Church. It could also have an origin in Greek mythology: Achilles was the main hero of the Trojan War and the strongest, swiftest and most handsome warrior of Homer's Iliad. Son of Peleus, king of the Myrmidons in Phthia, and of Thetis, a sea nymph, he was considered invincible but not immortal.

It is also recorded that Chiletti, Chilesotti, Chillon, Chilloni and Chiloni could be derivatives of Achille, or of the name Michele (Michael).