The authors agree that this surname derives from the Germanic name Grimaldo, documented from the year 666 in the figure of the Lombard king Grimoald(us) and frequent from the 8th century also in the forms Grimaldus and Grimoldus. The name is formed from two Germanic elements: grima(n)-, with the sense "helmet with a visor, combat mask", and waldaz-, with that of "mighty, prince or chief", giving the combined meaning "mighty with the helmet" or "helmeted chief".

E. De Felice notes that Frankish, Saxon and Provençal influences were superimposed on the Lombard tradition, with parallel forms such as Grimaud, Grimaut or Grimault. Among the regional variants, he stresses that Grimaudo predominates in north-western Italy and in Sicily, Grimod in the Aosta Valley, Grimoldi in Lombardy and Grimaudi in Emilia.

E. Rossoni adds that the surname may also derive from the place name Grimaldi, a locality in the Cosenza area, or from the place name Grimaldi di Ventimiglia, in the province of Imperia. He further notes that the variant Grimoldi is characteristic of the Milan, Varese and Como areas.

F. Miranda specifies that the place name Grimaldi, a comune in the province of Cosenza, would have taken its name from the Lombard king Grimoald himself (Cividale del Friuli, c. 600–671), duke of Benevento and king of Italy between 662 and 671. For his part, F. De Laurentiis proposes an alternative etymology: that the base is not the given name but the term grimaldo in its sense of an iron tool for opening locks without a key, associated with blacksmiths or thieves.

V. Blunda confirms the Germanic root and adds that the House of Grimaldi has ruled the principality of Monaco since 1297. The surname is found throughout Italy, with a particularly marked presence in Campania, Sicily, Apulia, Lazio, Lombardy and Emilia-Romagna.