The surname has multiple independent clusters of origin (ceppi), arisen in different regions without direct relation between them.

E. De Stefani proposes that the surname originated as a Friulian affectionate form of the feminine given name Adelaide, very widespread in medieval times. The Friulian form Adaleita would have been shortened to Leita, and then became a surname. Adelaide is of Germanic origin, formed on the roots athal ("nobility", in Old High German) and heit ("manner", "conduct"). De Stefani documents families bearing this surname in Pieria, a hamlet of the comune of Prato Carnico, in Carnia —the mountainous area of northern Friuli, in the province of Udine—, from the middle of the 17th century.

E. Rossoni identifies two areas of presence: one in Pasian di Prato, in the Udine area, and another in the region of Trentino-Alto Adige, with possibly distinct origins. For the Trentino-Alto Adige core, Rossoni suggests that it could derive from the Cimbrian word leit or lait, meaning "slope", alluding to characteristics of the terrain of provenance. The Friulian core, by contrast, is of uncertain origin for Rossoni, although he does not rule out that it shares the same root.