From the word "testa" = head, derived from the Latin "testam" = shell, used as a nickname for physic or intellectual characteristics.

The authors agree that this surname derives from a medieval nickname and name testa, based on the Latin word testa. S. Vannozzi specifies the semantic evolution: in Latin, testa originally meant "shell" or "husk", then came to designate a "terracotta vessel" and, by analogical extension taken from the colloquial language of the comic actors of the late Roman Empire —later taken up by the commedia dell'arte—, came to mean "head". This semantic path explains the two fundamental senses of the nickname: the literal one, referring to the head as a part of the body, and the figurative.

As for the figurative meanings, the authors provide complementary nuances. E. De Felice notes that, besides the physical sense, the term functioned as "individual, person" or alluded to "individual intellectual qualities", and that in southern Italy it also acquired the specific meaning of "terracotta container or vessel". F. Miranda adds that the nickname could have been born with a humorous tone from that same original Latin sense, and recalls that the Testaccio hill in Rome is formed from the debris of vessels of ancient Rome, which illustrates the currency of that meaning. E. Rossoni stresses that the nickname could also refer to a physically large head or to authoritarian attitudes, and documents its transformation into a surname in Pavia from 1418.

On the geographical distribution, the authors agree that the surname is present throughout Italy. De Felice notes a greater frequency in Liguria and in the Naples area. Miranda highlights its presence in Lombardy, Piedmont, Lazio and Campania, and documents a wide distribution in Sicily, with specific zones in the provinces of Catania, Palermo, Enna, Messina and Syracuse. Vannozzi also notes a notable concentration in Cercemaggiore, in the Molise region, where the surname is documented at least from the 16th century.

The surname presents multiple independent stems of origin (ceppi), arisen in different regions without a direct relation between them. Rossoni specifies the distribution of the variants: Testi is typical of Lombardy, the Verona area, Emilia, Tuscany and the Perugia area; Testini has a stem in the Sondrio area and the north of Brescia; Testino has a stem in Genoa and another in the Bari area; Testoni has stems in the Como, Bologna and Sassari areas. De Felice adds that Testoni is very common in Emilia-Romagna and that Testi is characteristic of Tuscany, while the compounds of the south have also spread towards central Italy. Vannozzi also mentions the derivatives Testina (small head), Testone and Testagrossa (big head) and Testarossa (red hair), all formed from physical or figurative characteristics related to the head.