You might wonder what the specific relation is between certain members of your family. Not only is it fun to learn the correct terms to use when referring to familial relationships, but it can also help you feel more connected to your family. Furthermore, research indicates that when you feel connected with friends and family, your physical and emotional health benefit from the close connection, according to Alexander Spradlin in the Psychology Today article, "The Importance of Staying Connected with Friends and Family."
Great-Nephew or Grandnephew
If your grandchild is male, then your grandson is a great-nephew to your brother, and your brother is your grandson's great uncle. The first known use of great-nephew, according to Merriam-Webster.com, was circa 1581. Some families prefer to use the term grandnephew, instead, which is a British term, according to Merriam-Webster.com. The first known usage of grandnephew is circa 1639.
Great-Niece or Grandniece
If your grandchild is female, then your granddaughter is a great-niece to your brother, and your brother is her great uncle. The first known use of great-niece, was 1884, Merriam-Webster.com notes. As with grandnephew, some families prefer to use the British term grandniece instead of great-niece. The first known use of grandniece was 1804.