The authors agree that this surname derives from the term chierico, which in the Middle Ages designated different realities: "priest or religious" (in opposition to the layman), "the one who serves mass and other sacred functions", and also "man of studies, lettered person or student of the medieval universities". The name, used originally as a nickname or a denomination of office or religious condition, is frequent from the 12th century.

E. De Felice notes that the name is documented in Latinised forms —Chiericus, Chericus, Clericus— in Turin, Genoa, Florence and Siena. He adds that the variant Clericò, with Greek accentuation, is peculiar to Calabria.

Both authors agree that the surname is spread in Tuscany and, with greater presence, in northern Italy, where the variant Chierego and its derivatives are peculiar to the northeast of Italy, in the regions of Veneto, Friuli-Venezia Giulia and Trentino-Alto Adige.