There are certain relationships that have specific names. The father of one of your parents is your grandfather. The mother of one of your parents is your grandmother. The sister of one of your parents is your aunt. And, you guessed it, the brother of one your parents is your uncle. But what about the brother or sister of one of your grandparents? That’s where things get a bit fuzzy.
Technically, the sister of one of your grandparents is your grand-aunt. “Grand” shows that it is one generation away; “great” is supposed to be added to generations beyond “grand.” But like so many other words in the English language, there’s the dictionary definition and then there’s how it’s commonly used.