The term "kokushu" was derived from "kunimochishu" (one of honorary terms for local governors who were in hereditary vassalage to the Shogun) of the medieval Muromachi period, who were shugo (provincial constables) of large provinces but whose family lineage did not make them kanrei (shogunal deputy) or goshobanshu (members to escort the Shogun).
大国守護でありながら管領や御相伴衆にならない家柄をさす中世室町時代の国持衆が語源。