The authors agree that the surname was formed from the name Angelo, derived from the ecclesiastical Latin angelus, an adaptation of the Greek ánghelos, which translates the Hebrew mal'āk ("messenger of God").

E. De Felice specifies that the name includes the variants Angiolo and Agnolo (the latter Tuscan and also Venetian). It continues in part the Late Latin name, of Christian milieu, Angelus, but is mostly formed in the Middle Ages from the noun ángelo —and ángiolo, ágnolo—.

De Felice notes that the surname is widespread throughout Italy in the types Angelo and, less frequently, Angiolo. The patronymics in De and D' are peculiar to and very common in the south, especially in the Naples area. The type Agnolo is characteristic of Tuscany and the Venetias (and Agnelutto, of Friuli-Venezia Giulia). The compounds are specific to the south.

E. De Stefani suggests that the surname originated as a derivative of the mother's name, from the feminine given name Angela. He notes that in the families of Cesclans, for centuries the surname was written Agnula and later passed to its masculinised form Angeli.

De Stefani adds that Angelus was used as a given name as early as among the first Christians, and that in medieval times it was used to indicate the archangel Michael. Over time it became a surname.