Your grandfather's sister is your great aunt.
Lets explain this step by step as so many people get all this genealogy family stuff mixed up 1.Your Grandfathers niece(this would have to be your grandfathers brother(your great uncle),or sister(your great aunts)daughter to be your grandfathers niece. 2. This niece of your Grandfather would be the first cousin to your mother or father, 3. This niece would be your "SECOND COUSIN"
its your mothers or fathers cousin (or second cousin)
Your grandfather's sister is your great aunt.
Just as your dad's sister is your aunt, your grandfathers sister is your great aunt.
They would be your aunts and uncles, as they are your mother's or father's brothers and sisters.
He is your Great grandfather.
Aunty
Most likely they would not be related to you
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
What is my godfathers niece to me
For clarity, lets call your great great grandfather's niece "the niece". The relationship sequence: (1) The niece is the daughter of your great great grandfather's sibling (2) The niece is a 1st cousin of one of your great grandparents (3) The niece is a 1st cousin once removed of one of your grandparents (4) The niece is a 1st cousin twice removed of one of your parents (5) The niece is your 1st cousin three times removed
cousin
Your niece's brother is your nephew.
Your son and your niece are first cousins.
3rd cousin
Nothing. Your niece in law. Your brother in laws niece.
Your great great grandfather.
cousins
your niece