Family nickname. Second only to personal nickname. Because this is Banat and that's how it goes. Mostly it was invented in villages with just three surnames, so the different branches would have different names, at least unofficially. Official wouldn't cut it, because just like personal nicknames, these were often mockery. For instance, in granma's village, one branch of some family was Vukini, and the other Zajeci (related to wolves and rabbits). The final form was Vukonje and Zaječonje. Another such was Zaparin (zapara is the muggy weather, too hot and humid), Kaljugin (mire's), Šaragljin (šaraglje is the rear side of a horse cart). Bakrač is a copper kettle (bakar - copper), Kakin (kaka is caca, same in many languages).
There were funny cases when one guy's špicnamet was another guy's actual surname - you'd ask yourself is this other guy for real. In many cases I wouldn't know the real surname (or even name) for years, it was never needed theretofore.
20-VII-2020 - 26-II-2026