The authors agree in noting that this surname derives mainly from the hypocoristic Nanni (or Nanne), an affectionate and dialect form of Giovanni, arisen by aphaeresis and phonetic simplification of the name. Its distribution is concentrated in central Italy, with a particular presence in Tuscany, Lazio and Emilia-Romagna.

E. Rossoni specifies that the surname would derive from an adaptation by syncope of Giovanni, with an important core between Emilia, the Marche and Tuscany. E. De Felice adds that the variant Nani, with a single n, is proper to northern Italy —frequent in Emilia-Romagna and Veneto— and that the form Nanùt is specific to Friuli-Venezia Giulia. He further notes that Nani may reflect, in some cases, a nickname related to the term nano ("dwarf"), independent of the etymon of Giovanni.

P. Canè recalls that Giovanni is a name of Hebrew origin diffused in the Christian tradition, which places the surname within the broad family of patronymics derived from that name.

V. Blunda proposes for Sicily a different origin: the surname would come from the Sicilian dialect word nànnu, with the meaning "grandfather" or "elderly relative", and would have arisen as a byname applied to the descendant of the eldest of the family line.