þriðjungi

Þriðjungi refers to the third-generation owners of small farms or rural settlements in Iceland during the Húsabúk system, which prevailed from the mid-16th to the late 18th century. These owners typically inherited land and other assets from their parents or relatives.

In the Húsabúk system, each farm was assessed based on its productive value, with large farms securing 20-25 "tax units" and small farms a single unit. Tax units were used to determine the amount of tax owed to the chieftain or lord, and were adjusted according to changes in the size or productivity of the farm. Þriðjungi, having only a single tax unit, represented the lower end of the productive scale.

There were two main types of þriðjungi in late 16th-century Iceland: those who inherited only a small farm or a single tax unit from their fathers, and those who owned several scattered parcels of land. The former of these two groups were generally exempt from taxation due to their low means, while the latter were typically required to pay taxes on all their holdings regardless of their overall tax burden.

By the late 18th century, the Húsabúk system was largely dismantled by the Icelandic chieftains in response to elite competition and final sweeping economic changes.