The authors agree that this surname derives from the personal name Rinaldo, of Germanic origin. Its etymon points back to two roots: ragin or ragan, with the sense of "divine counsel," and wald or waldaz, with that of "to govern, to command," so that its approximate meaning would be "one who commands with divine counsel." E. De Felice documents the name in Italy from the 9th century and notes that the form Rinaldo prevailed over the others in the late Renaissance through the influence of the character of the same name in the Gerusalemme liberata of T. Tasso.

F. De Laurentiis stresses that the name arrived in Italy from France, where it circulated as Renaut or Rainaut in the chivalric epic, and that the Lombards introduced it in the form Reginaldo. F. Miranda specifies that the medieval Latin name Raginaldus was already used among Goths, Lombards, Saxons and other Germanic peoples, and that from the Norman period it began to function as a patronymic surname. R. Brondolo adds, for the Naples area, the curious tradition according to which the Rinaldi would descend from the cantastorie who recited the Rinaldo, popularly known as cantarinaldi.

De Felice details the main regional variants: Rinaudo, Ranaudo and Reinaudo are proper to the north-west and in part to the far south; Rainoldo and Renoldo, to the north; and forms such as Rinavolo, Renauro or Renaulo, to the Neapolitan and Sicilian area. The surname is diffused throughout the Italian peninsula and is one of the most frequent in the country.