Meaning of "great-" in Essential English Dictionary

great-

prefix uk /ɡreɪt/
great-grandfather/-grandmother
great-aunt/-uncle

the aunt or uncle of your mother or father

great-grandchild, -granddaughter, etc.
great-niece/-nephew

the daughter or son of your niece or nephew

(Definition of “great- prefix” from the Cambridge Essential Dictionary © Cambridge University Press)