matrilateral
/ˌmatrɪˈlat(ə)rəl/ /ˌmatrɪˈlat(ə)r(ə)l/Cultural Anthropol.
adjective
Of, relating to, or designating a relationship (especially a marriage between cousins) in which a mother and one of her siblings or other relatives are both involved as parents.
Origin
1950s; earliest use found in Journal of the Royal Anthropological Institute. From matri- + lateral. Compare earlier patrilateral.