The authors differ on the origin of this surname. A. Bongioanni links it to the Latin given name Celsus, which means "tall", and notes that Saint Celsus was a martyr in Milan around the year 68, together with Saint Nazarius, whose feast is celebrated on 28 July.

V. Blunda offers a different interpretation circumscribed to Sicily. He considers that it is a surname of dialectal origin belonging to the group of phytonymic surnames —that is, derived from names of plants—. It derives from the dialectal word ceusu, meaning "mulberry" or "mulberry tree", a tree widely cultivated in Sicily during the Middle Ages for the raising of silkworms, an activity introduced by the Arabs and consolidated during the Norman period. For Blunda, the association with the Latin name Celsus constitutes a false popular etymology. The surname could have originated in a place name applied to the one who lived near a mulberry tree, or in the trade of the silk-grower.

Both interpretations are not necessarily mutually exclusive: the surname could present independent clusters of origin arisen in different regions without direct relation to each other.