The authors agree in noting a Germanic base for this surname, although they differ in the details. There are several hypotheses of origin: a derivation from the Austrian surname Fritscher, another from the Gothic name Frigeridus, and a third —considered the most probable given its geographical concentration— from the Late Latin frigerius ("the one who makes cool"). It is also noted that Frigerio, together with the variants Frigeri, Frigieri, Fruggeri and Forghieri, reflects the medieval name Frigerius or Frogerius, of Frankish derivation. Its diffusion is characteristic of Lombardy, with presence in the Varese, Como, Lecco, Bergamo, Brescia and Milan areas.

V. Blunda offers a different etymology: he derives the surname from the Germanic compound Frithu-Gairu, formed by frithu ("peace", "truce") and gairu ("spear"), meaning "spear of peace" or "peaceful spear". According to Blunda, this apparent contradiction reflects a Germanic anthroponymic conception in which peace was not simple absence of conflict, but a juridical order guaranteed by the one who bore arms respecting the pacts. Blunda agrees that the surname is preserved mainly in Lombardy and the Alpine zones of northern Italy.