The authors agree that the surname originates in a nickname, though they differ on the exact lexical base. E. Rossoni proposes two hypotheses. The first refers to the Lombard-Venetan dialectal word trapel, which means both "small deception" and "new shoot of the vine", possibly attributed with an affectionate tone to the surname's founder. The second points to the archaic term trapello, a canvas with hooks used to drag heavy objects, which would suggest an origin related to the trade of porter.

F. De Laurentiis proposes instead that the base is the nickname trapelo, used in a figurative sense to designate the "horse or other draught beast that reinforces a vehicle on a climb". Both etymologies refer to a context of physical effort or labour.

Rossoni locates the main form of the surname in the Ferrara area —with a presence in localities such as Mesola, Codigoro and Jolanda di Savoia— and in the Rovigo area, with a secondary nucleus in Rome and Latina. The variants Trapelli, Trappella and Trappelli are scarce or exceptional, and are documented in zones of Brescia and in Emilia-Romagna.