The authors agree that the surname derives from the personal name Germano, which prolongs the imperial Latin cognomen Germanus. E. De Felice notes that this term may reflect two distinct meanings: the gentilic Germanus ("inhabitant or native of Germania; belonging to a Germanic people") and the adjective germanus ("brother of full bonds, born of the same parents"), a sense that in the Christian context evolved towards "brother in Christ, in the faith").

E. Rossoni broadens the range of possible origins and includes, besides the medieval name and the Byzantine name Germanus, the Germanic ethnic identifier, the term germano meaning "brother of someone" and place names such as Germagno or San Germano —present-day Cassino— in the Frosinone area.

De Felice documents regional variants: Germàn in Veneto, Germanaz in Valle d'Aosta, Iermano and De Germano in southern Italy, and apocopated forms with a Greek accent in Calabria and Sicily. Rossoni, for his part, places the surname throughout centre-northern Italy, with a notable presence in Lazio and in Trieste, while the variant Germano shows specific zones in Piedmont, Liguria, the Frosinone area and southern Italy.