The authors agree that this surname derives from the dialectal word spanu or spano, though they differ on its etymology and on the meaning attributed to that base.

E. De Felice considers it a Sardinian surname, arisen from an old nickname formed from the Campidanese spanu and the Logudorese ispanu, meaning "reddish, light red", originally referring to the coat of horses and later applied to people, alluding to the colour of hair and beard. For occurrences of the surname outside Sardinia, he refers to the variant Spanò.

E. Rossoni offers a broader perspective. In Sardinia, he notes that spanu means "yellow, light brown" —a sense that differs from the one proposed by De Felice— and documents the surname from the High Middle Ages, in the Judicate of Gallura: its first recorded mention dates from 1113, when the judge Comita Spano made a donation of lands to the cathedral of Pisa. Outside Sardinia, Rossoni also extends it to the Apulia region, and specifies that the variant Spanò is predominantly Sicilian and Calabrian, while Spanu is specific to Sardinia.

G. Rohlfs proposes a different etymology: according to him, the surname is of Greek-Byzantine origin, and in Calabrian dialect spanu means "beardless, smooth-faced", derived from the Greek σπανός. He records it in the city of Catanzaro and its province —including the Crotone area— as well as in Campania and Apulia. He refers to the variants Spanò and Sbano.

P. Durante also notes the Greek origin of the surname, without developing further detail.

V. Blunda approaches it from Sicilian dialect: the word spànu there described a person with thin hair or areas of partial baldness, and the surname would have arisen as a nickname applied to someone with that visible physical trait.

In sum, the base spanu / spano appears in different dialectal traditions with partly divergent meanings: "reddish" in Sardinian according to De Felice, "yellow or light brown" according to Rossoni, and "beardless, smooth-faced" in the Calabrian and Greek area according to Rohlfs and Blunda. The geographical distribution of the surname covers mainly Sardinia, but also the Apulia region, Sicily and Calabria.