The authors agree that this surname has its origin in the medieval Latin term clericus, which designated a man linked to the Church but not ordained a priest. The surname would have been formed from the one who was the son of a cleric or was one himself. E. Rossoni notes that the ending in -ato, peculiar to the Veneto, and in -ati, peculiar to Emilia and eastern Lombardy, frequently have a patronymic value, equivalent to "son of". He also documents traces of the transformation into a surname at the beginning of the 16th century in Fabriano.

F. De Laurentiis specifies that the lexical base is the noun chierico —in Venetan dialect: chierego—, which could refer both to an ecclesiastic or aspirant to the priesthood and to a learned or educated man. He also adds the form chierica —in dialect chierega—, which designated the circular shaving on the crown characteristic of clerics, which allows the surname to derive likewise from a nickname linked to physical features.

Rossoni distinguishes several forms with differentiated geographical distribution: Chieregati is peculiar to the Rovigo area, especially to Trecenta; Chieregato presents areas in Chioggia and in Badia Polesine; Chiericati, very rare, appears in the zone that covers the upper territory of Modena, the Mantua area and that of Ferrara; Chiericato, also very rare, is characteristic of the Verona and Padua area. The forms Chierigati and Chierigato are considered variants arisen through transcription errors.