The authors differ on the origin of the surname. E. Rossoni maintains that both Cardi and its related form Cardo would derive from abbreviated forms of the name of Germanic origin Ricardo. According to Rossoni, Cardi is scattered in central-northern Italy, with notable presence in the Ferrara, Bologna, Florence, Rome and Latina areas; while Cardo presents clusters in the Benevento area, in the region of Campania, and in the Naples area, in addition to another in the Bari area.

F. Miranda, on the other hand, proposes a different origin: both Cardi and its accented variant Cardì would derive from the Greek kardion or from the Late Greek kàrdos, meaning "thistle" (in Latin, carduum), a spiny plant of the aster family, with flowers similar to those of the artichoke. Miranda notes that Cardì, a rarer form, appears in Sicily —specifically in the province of Enna—, as well as in Lazio, Tuscany, Piedmont, Lombardy and Trentino-Alto Adige. Its variant Cardi, more widespread, has presence mainly in northern Italy, Emilia-Romagna, Lazio, Tuscany, Veneto and Lombardy, with specific areas also in Sicily and Sardinia.