The authors agree that the surname is composed of two elements: cao, a dialectal form of capo ("head" or "beginning"), and duro ("hard", "rigid"). However, they differ in the interpretive emphasis. E. Rossoni notes that it would derive from a nickname alluding to the obstinacy of the founder of the lineage, to episodes of physical resistance in combat, or to the place of origin of the family. As the most probable toponymic origin, Rossoni identifies a contrada called Caoduro —that is, Capo Duro—, mentioned in a lease contract of a mill in the Contrà Caoduro of Barbarano Vicentino, signed in 1538.

F. De Laurentiis considers it a surname typical of the Ferrara area and emphasises the nickname value of the expression: the original nickname would allude to someone who had a difficult beginning and did not yield in the face of adversity. De Laurentiis also notes that a toponymic origin cannot be ruled out, since it is frequent to find areas called Cao di sotto ("beginning below a small height"), in reference to the beginnings of areas with steep terrain.

As for the geographical distribution, Rossoni documents the surname mainly in the Veneto: in the Vicenza area —in localities such as Vicenza, Monticello Conte Otto and Montecchio Maggiore— and in the Treviso area, in Giavera del Montello. The variant Cauduro appears also in the Treviso area, in Volpago del Montello.