There are a few synonyms for the name "Giovanni Vincenzo Pecci." One synonym might be "Gianni" for short. Another possibility might be "Vinnie" as a nickname. In terms of related names, Giovanni and Vincenzo are both Italian boy names that can be used independently. Pecci might also be a synonym for the Pecci family, which was a powerful noble family in Italy during the Renaissance period. Overall, while there aren't many direct synonyms for the name Giovanni Vincenzo Pecci, there are plenty of related names and nicknames that could be used in various contexts.