The authors agree that this surname derives from the Germanic given name formed by the roots gaira or ger ("spear") and hardhu or hard ("hard, strong"), with the general sense of "strong with the spear" or "valiant spearman".

A. Bongioanni notes that the name gave rise to numerous derived surnames of evident etymology, common to all Italy: Gerardi, Gherardi, Ghirardi, Girardi, Giraldi, together with forms such as Giraudi, Girodo, Girodetti, and possibly Giretti —of Piedmontese origin— and Girardengo, considered a patronymic. He also mentions Saint Gherardo, bishop and patron of Velletri, whose feast is celebrated on 7 December.

V. Blunda, who places the surname in Sicily, provides the hagiographic fact of Saint Gerard Sagredo (c. 980–1046), a Venetian bishop sent by King Stephen I of Hungary to evangelise the region of Csanád, where he suffered martyrdom during a pagan revolt and became patron of Budapest. The Gellért hill —the Hungarian name of the saint— dominates the city over the Danube. Blunda attributes to the diffusion of his cult the expansion of the name throughout central Europe.