The authors agree that this surname derives from the personal name Nazario, of Christian origin. A. Bongioanni notes that Saint Nazarius was a martyr venerated at Milan together with Saint Celsus in the year 68, whose feast is celebrated on 28 July. In the Venezia Giulia area —that is, north-eastern Italy, in the regions of Veneto, Friuli-Venezia Giulia and Trentino-Alto Adige— Saint Nazarius, bishop of Capodistria between the years 524 and 557, acquired special devotion, celebrated on 19 June. Bongioanni also documents the Piedmontese variant Nasario and the form Nazari.

E. Rossoni specifies that all the variants derive from the name Nazareno or from its derivative Nazario, very widespread in the late Middle Ages, with documentation in the Codice Diplomatico della Lombardia Medievale in a deed of 1093. Rossoni also considers a possible derivation from place names such as San Nazario, present in the Salerno and Vicenza areas. As for the geographical distribution of the variants, Nazaro is proper to Puglia —especially Gallipoli, in the Lecce area, and the Taranto area—; Nazarri is specific to the Milan area; Nazzari is Lombard; and Nazzaro corresponds mainly to the region of Campania —the Naples, Benevento and Avellino areas—, with a presence also in Rome and in the Foggia area.