F. Miranda and V. Blunda offer different interpretations of the origin of the surname Giachino. Miranda considers it part of the large family of surnames derived from the personal names Giacomo and Jacopo, which originated from the Hebrew Ya'aqov. According to this view, the surname developed through contractions, dialectal forms and diminutives that became hereditary over time, a common process in medieval Italian onomastics.

Miranda also proposes alternative possibilities. The surname could be connected to the medieval term giacco, a type of padded or mail coat worn by soldiers for protection, thus originating as an occupational or descriptive nickname. He further suggests that some branches may derive from the Italianization of the French personal name Jacquin or from the Hebrew name Jakim.

V. Blunda, by contrast, proposes a specifically Sicilian origin. In his interpretation, Giachino derives from the dialect form jachìnu, a popular shortened version of the name Gioacchino (Joachim), traditionally identified as the father of the Virgin Mary. The alternation between the initial g- and j- is a characteristic phonetic feature of the Sicilian language. Under this hypothesis, the surname originated as a patronymic, identifying the descendants of a man named Gioacchino.

According to Miranda, the surname is particularly associated with Piedmont, although branches are also found in Sicily, Liguria, Lombardy, Tuscany and Veneto. Overall, Giachino appears to belong to the broad group of surnames derived from personal names related to Giacomo, Jacopo or Gioacchino, while preserving regional linguistic influences that shaped its modern form.