Relating to a grandfather or the paternal line of grandparents; characteristic of paternal grandparents or their role.
From grandpa (informal grandfather) plus -ternal (from paternal, meaning 'of the father's line'). This is a rare, technical term created to distinguish the grandfather's side specifically.
Grandpaternal is so obscure that most dictionaries don't list it, yet it fills a real gap—you can say 'maternal grandmother' and 'paternal grandfather,' but grandpaternal is the word nobody uses!
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