E. De Felice, F. De Laurentiis and R. Brondolo agree that the surname Guidi derives from the personal name Guido, a name of Germanic origin that became widely established in Italy during the Middle Ages. The earliest forms, Wido and Wito, are documented as early as the 7th century during the Lombard period.

According to E. De Felice, the Italian forms Guido and Guidus appeared from the 9th century onward and became especially popular between the 11th and 12th centuries under Frankish influence. The name is generally considered a shortened form of older Germanic compound names containing the elements *widu- (“wood” or “forest”) or *wida- (“distant” or “wide”). As a result, the original meaning may have been associated with forests, woodland environments, or broad and far-reaching qualities.

F. De Laurentiis confirms that the name was introduced into Italy by the Lombards and gradually adapted to local linguistic traditions. Over time, it became one of the most widespread medieval personal names and eventually gave rise to numerous hereditary surnames.

R. Brondolo also supports the Germanic origin of the name and emphasizes its connection with the meaning “forest,” although without proposing additional etymological details.

The surname Guidi is particularly common in Emilia-Romagna, Tuscany, Lombardy and Liguria. Related forms developed in different regions, including surnames beginning with Ghid-, which are especially frequent in Lombardy and Emilia-Romagna, and Ghio, characteristic of Liguria and Piedmont, possibly influenced by the French name Guy. Together, these variants reflect the long-standing diffusion and regional adaptation of one of medieval Italy’s most enduring Germanic personal names.