An uncle of one's grandparent (i.e. a brother or brother-in-law of one's great-grandparent)

A great-granddaughter of one's sibling, a granddaughter of one's nephew or niece. (Brother's great-granddaughter: fraternal great-grandniece. Sister's great-granddaughter: sororal great-grandniece)

A great-grandson of one's sibling, a grandson of one's nephew or niece. (Brother's great-grandson: fraternal great-grandnephew. Sister's great-grandson: sororal great-grandnephew.)

plural of great-grandaunt