Your grandfather's great nephew is your second cousin.
Your grandfather's great nephew is your second cousin.
Your great grandfather's sister is your great great aunt. You are her great great niece or great great nephew, depending on your sex.
What is your great-great-great grand nephew?!
Your grandfather's nephew would be your First Cousin once removed Ref: http://freepages.genealogy.rootsweb.ancestry.com/~gentutor/chart.html
You're a Great Aunt to your nephew's son, who is your great nephew.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
Your nephew's grand son is your great great nephew and you are his great great uncle (or aunt)
She would be your great grandmother
You are your great nephew's great uncle or great aunt, depending on your sex.
The English language has no relationship name for the wife of your great niece or great nephew.
He would be your great-great uncle.
Your nephew's daughter is your great niece and you are her great aunt (if you are a woman) or her great uncle (if you are a man).