The presentation focuses on the duality of certain kinship terms when a term and a position in a kinship system named by it also mark a certain inferior status in a social hierarchy. The Arabian term umm-walad (‘mother-of-child’) was used in Islamic jurisprudence for a female slave/ a concubine who had children with her master and was considered a member of his family. This kind of kinship term functioned within Islamic legal rules system which legalized the institute of slavery. After the forced abolition of slavery in the colonial times, the abolition of this specific status led to a decay of umm-walad institute as an important component of traditional Arabian family and as a kinship term. The institute of suria (concubines, secondary wives) that implied possibilities for female slaves to rise to a higher social status of umm-walad (‘mother-of-child’) played an important role in the social structure of the pre-colonial Sultanate of Oman and in the genealogy of the Omani-Zanzibari ruling dynasty. Being a suria and/or umm-walad meant both a position in local social hierarchy and a position in the kinship system. Most Zanzibari sultans from the Omani dynasty al-Busaid originated from suria-mothers. Becoming an umm-walad provided a means of socialization among the free-born and integration into Arabic families. The abolition of slavery and the further abolition of the institute of suria / umm-walad as an element of slavery was much opposed among Zanzibari nobility since this important component of local family and kinship system was deemed illegal.