The consulted works concur in tracing Monari to an occupational origin, deriving it from the Italian term molinaro, meaning "owner or manager of a mill." F. De Laurentiis notes that the surname is diffused in northeastern Italy, in the regions of Veneto, Friuli-Venezia Giulia, and Trentino-Alto Adige, as well as in part of Emilia-Romagna, and identifies its formation as the transformation into a surname of a name or nickname rooted in that occupational term.

P. Canè agrees on the occupational origin and adds a comparative note, observing that this surname corresponds to the trade of miller in the same way as surnames such as Miller in English or Müller in German. It is also recorded, more concisely, as deriving from the words mugnaio and molinaro, both meaning "miller."