noun
A granddaughter of one's sibling; a daughter of one's nephew or niece. (Brother's granddaughter: fraternal grandniece. Sister's granddaughter: sororal grandniece.)
"My brother's granddaughter, Lily, is my grandniece. "
grandniece
/ˈɡrænˌniːs/ /ˈɡrændˌniːs/